Skip to main content

Sleep Cycle and Sleep Waves-Stages,Length,Disorders,sleep app

Sleep Cycle and Sleep Waves-Stages,Length,Disorders

Sleep is naturally recurring states of reduced or absent consciousness and suspended sensory activity from which a person can be aroused by sensory or other stimuli. The whole process of sleep is completed in multiple series of cycles known as sleep cycle with different changes in cerebral activity recorded by an electroencephalogram as sleep waves.


Overview of sleep Cycle

  • Introduction of Normal sleep cycle
  • 2 types of sleep
  • 4 stages of sleep cycle
  • Sleep waves
  • Sleep cycle length
  • Sleep Cycle length by age and weight
  • Sleep disorders
  • Effect of Electronic on sleep cycle
  • Do sleep cycle monitoring app works?


What is Sleep Cycle? (Introduction)

Soon after a person sleep, they go through a series of REM and non-REM type of sleep stages which completes their one sleep cycle. In the night there are multiple cycles of sleep which is of 90 minutes each.

In humans the sleep/wake cycle is controlled by light by activating the suprachiasmatic nucleus. The suprachiasmatic nucleus is a small bundle of neurons located in the hypothalamus.

Melanopsin receptors in the retina of the eye respond to the presence or absence of light by transmitting signals to the suprachiasmatic nucleus via the optic nerve.

Light induced activation of the suprachiasmatic nucleus prevents the pineal gland from producing melatonin, a hormone that otherwise signals biological night and creates the onset of sleepiness in contrast and absence of light results in the suprachiasmatic stimulating the pineal gland to produce melatonin, which is released into the blood.

Usually this occurs around 9:00 pm as a result melatonin levels in the blood rise sharply and you begin to feel less alert and sleep becomes more inviting. Melatonin levels in the blood stay elevated for about 12 hours all through the night before the light of a new day when they fall back to low date home levels by about 9:00 am.

This is how sleep cycle works in human and regulates the rhythm of sleep/awake state in body in a duration of 24 hours.


Types of sleep

When person fell asleep, he goes through multiple series of slow-wave sleep (NREM) and Rapid eye movement sleep (REM), alternating with each other.

Slow-wave Sleep: it is also known as non-rapid eye movement sleep. it occupies about 75 % of total sleep. this sleep is also known as deep sleep which is of most restfulness. This sleep is associated with a decrease in vascular tone and different vegetative function of body adding to maintain normal Homeostasis.

Dreams are unlikely to occur during NREM sleep so they are also called as “Dreamless Sleep” but some may be present sometimes. Those dreams are not remembered as consolidation of those dreams do not occur in the brain. It is the sleep that is experienced in the first hour of sleep after a long duration of wakefulness and mostly theta waves are associated with this type of sleep.

Rapid Eye Movement Sleep: In it, there is the rapid and continuous movement of eyes even though the person is in complete state of sleep. It is an active form of sleep associated with vivid dreaming. REM sleep occurs in episodes during whole sleep duration and covers about 25% of total sleep duration in adult.

During REM sleep brainwaves mimic the activity of the brain of an awake person. They are very similar, both containing high-frequency beta waves. The rapid eye movement in this sleep is a result of the intense stream and brain activity that occurs during this stage. It is during this stage of sleep that vivid and powerful dreams usually occur and muscle is paralyzed. Scientists believe this may be to help prevent others from injury while trying to act out her dreams.

This stage is also characterized by an increase of the heart and respiration rates and their rhythms become irregular. One of the peculiar characteristics of REM stages is that it typically gets longer and longer as the night goes by and the last REM stage can last for an hour.


4 Stages of Sleep cycle

Sleep stages are defined based on the measurement of electrical activity in the brain using an electroencephalogram, or EEG. An EEG represents fluctuations in brain electrical activity in voltage as a waveform of variable frequency and amplitude.

The American Academy of Sleep Medicine classifies sleep as consisting of 4 stages. The first two stages involve drowsiness and light sleep. When someone begins to fall asleep, they enter:

Stage 1: During this stage, an EEG records low-amplitude waves of mixed but mostly high frequencies. Stage 1 sleep is the transition from wakefulness to sleep which typically lasts between 10 to 15 minutes. it is a light sleep where you drift in and out of sleep and can be easily awakened indeed.

If awakened in this stage, a person will claim they were never actually asleep. In this stage

  • Theta waves appear on the EEG,
  • The eyes move slowly,
  • Muscle activity slows during this stage,
  • Many people experience sudden muscle contractions preceded by a sensation of falling these are known as hypnagogic jerks,
  • Breathing also slows down,
  • Heartbeat becomes regular in this stage.


Stage 2: When the person enters stage 2 sleep, this is characterized by the presence of phenomena on an EEG known as sleep spindles and K complexes. Sleep spindles are trains of high-frequency waves and K complex involves a biphasic wave that stands out from the rest of the EEG. Stage 3 sleep is also known as slow-wave sleep or deep sleep. Stage 2 is the main body of sleep and lasts 5 to 15 minutes. It is a light sleep during which

  • Memory consolidation occurs,
  • Eye movement stops,
  • Brain waves become slower with occasional bursts of rapid brainwaves known as sleep spindles,
  • K complexes also appear,
  • Heart rate slows down,
  • Body temperature decreases in preparation for deep sleep.


Stage 3: When a person enters stage 3, extremely slow brainwaves called delta waves are interspersed with smaller faster waves. As a result, this deep sleeps often called slow-wave sleep, which are low-frequency, high amplitude waves and makeup at least 20% of brain activity. Stage 3 sleep is thought to be especially important to overall restfulness. It is during this stage that a person may experience

  • Sleep walking,
  • Night terrors,
  • Talking during one's sleep,
  • Bedwetting.
  • These behaviours are known as parasomnias

Next, the sleep passes rapidly back through stage 2 and stage 1 before entering the rapid eye movement or REM sleep.

Stage 4: In stage four, deep sleep continues as the brain produces delta waves almost exclusively at this point. You will sleep through most potential sleep disturbances such as noises and move without showing any reaction and being awoken during slow-wave sleep will result in a few minutes of disorientation.

Deep sleep reduces your sleep drive and provides the most restorative sleep of all the sleep stages. This is why, if you take a short nap during the day, you're still able to fall asleep at night but if you take a nap long enough to fall into a deep sleep you have more difficulty falling asleep at night because you reduced your need for sleep.

Finally, after these stages on NREM, cycle person passes in REM sleep. In REM sleep, EEG activity resembles what’s seen in stage 1 or restful waking. During REM sleep, the muscles are completely relaxed and limp but the eyes are moving rapidly. This is the time of sleep when our most vivid dreams are likely to occur. After REM sleep, the person will sometimes awaken briefly but then will move through the sleep stages again, in order. Most people will repeat this cycle 4-5 times a night, with each cycle lasting about 90 minutes.


Stages of sleep



Sleep Waves


Stage 1

The transition from awake to sleep.

10-15 min

Alpha and Theta

Slow breathing and heart rate

Relaxation of muscles

Hypnogogic jerks

Stage 2

Initial light sleep

5-15 min

Sleep spindles and K-complex

Slow breathing rate

Fall in body temperature

Simple plot dreams

Stage 3-4

Slow-wave sleep/deep sleep

10-15 min


Dreamless sleep

Hard to wake

REM Sleep

Rapid eye movement sleep

15 min

May last an hour-long, as sleep progress


Vivid dreaming

Irregular heart rate and breathing pattern

Raise in body temperature

Body is paralyzed

Increase in blood pressure




Sleep Waves/Brain Waves in Sleep Cycle

Electrical recording of brain activity during sleep has shown different electrical activity of the brain during different stages of the sleep cycle. The intensity and pattern of brain activity depend upon excitation of the specific part of the brain during sleep. The undulation in the recorded electrical potential of the brain during sleep and wakefulness is called Sleep Waves.

The activity of a single neuron is not enough to be recorded all the way through skull. Hence these waves are the result of the summated activity of thousands and millions of neurons firing synchronously.

There are 4 types of brain waves known as Alpha, Beta, Theta and Delta waves associated with sleep and also especially known as sleep waves.

Alpha, Beta, Theta and Delta waves/Sleep Waves/Brain Waves in Sleep Cycle

Alpha Waves: These waves have a frequency of 8-13 cycles/sec with a voltage of about 50 microvolts. These waves rhythmic in nature and found in all normal person in the state of wakefulness and in quiet, resting state of cerebration. These waves are recorded by EEG mostly in occipital, parietal and frontal region for the scalp. These waves cannot be recorded during deep sleep as they completely disappear.

Beta Waves: These waves have frequencies of 14-80 cycles /sec. These waves are mostly recorded in the region of the parietal and frontal lobe of the brain. These waves frequently replace alpha waves when the attention of the awake person is directed to a specific type of mental activity. Those asynchronous beta waves are of higher frequencies and low voltage.

Theta Waves: These waves have frequencies of 4-7 cycles/sec. These waves are mostly recorded on parietal and temporal lobes. These waves are associated with emotion and are found in condition like frustration and disappointments. These waves are also indicative of many brain disorders and degenerative brain disease.

Delta Waves: These are universal waves as they include all the brain waves with frequencies of about 1-3.5 cycle/sec. These waves can be recorded in a very deep sleep stage in the cortical region of the brain. They have voltage 2-4 times greater than any other brain waves. Delta waves are independent of activity in the lower region of the brain hence can be recorded in the cortex of the brain independently.

Sleep wave transition as a person goes from Awake to sleep


How long is Sleep Cycle?

The first sleep cycle is about 90 minutes long and in an average, it is about 90-120 minutes long. A person completes 4-5 sleep cycle in one night and as sleep progresses it last longer.

Asleep cycle refers to the period of time it takes for an individual to progress through the stages of sleep. As just outlined, one does not go straight from deep sleep to REM sleep. However rather a sleep cycle progresses through the stages of non-REM sleep from light to deep sleep then reverses back from deep to light sleep, ending with time and REM before starting over in light sleep again. for example, the order looks something like this

  1. stage 1 light sleep
  2. stage 2 light sleep
  3. Stage 3 deep sleep or slow-wave sleep
  4. stage 4
  5. stage 3
  6. stage 2
  7. REM sleep

After REM sleep the individual returns to stage 2 of light sleep and begins a new cycle as the night progresses. Individuals spend increasingly more time in REM sleep and correspondingly less time in deep sleep.


Sleep Cycle length by age and weight

There is great impact of age and weight in the length of the sleep cycle. As in a child, the duration is more in comparison to adults. similarly, a fat person is more likely to have more duration of sleep than slim/thin person.

Study has shown that at different age of life body demand different duration of sleep. Such as



Sleep Duration


0-3 month


4-11 month

















Sleep is vital for baby's growth and development. Newborns will sleep on and off throughout the day and night, Waking often for feeding. Older babies aged 3 to 6 months might start moving towards a pattern of 2 to 3-day time sleeps up to 2 hours each. They may still wake at least once a night. By 6 to 12 months, babies may have their longest sleep at night. Though most this age will still have a daytime nap. Children will move through periods of light and deep sleeping and it may differ day to day depending on changes to its regular routine.

Similarly, in fat person usually, they have more sleep duration which is a result of obesity. Their body metabolism process slows down usually after meal time for metabolizing ingested food. Which make them sleepy all the day.


Sleep Disorders

Common Sleep Disorders Over 40 million Americans are thought to be dealing with some type of chronic sleep disorder. In addition to those numbers, there are millions who have to deal with occasional insomnia or disrupted sleep patterns. To date there are over 70 different types of sleep disorders with the most common being:

  • Insomnia
  • Sleep Apnea
  • Restless Leg Syndrome
  • Narcolepsy
  • Sleep paralysis
  • REM Sleep Behaviour Disorder
  • Exploding Head Syndrome
  • Kleine Levin Syndrome
  • Sleep Related Sleeping Disorder
  • Sexsomnia
  • Nocturnal Death Syndrome



It is the one that most people are familiar with. It is defined as experiencing poor quality of sleep and it includes not being able to fall asleep or to stay asleep. The basic definition of insomnia is that a person can't sleep well and there’s a daytime consequence. Could be the person’s irritable, they're tired, they're fatigued, they can't think right, so there's a really negative consequence to that bad night of sleep. Most adults have had a bad night of sleep before. Fortunately, most of us get right through it and the next night we're back on track but some people they develop really a chronic problem where they're just not rightly getting a good night of sleep. And so, we really work to try to undo that for people.


Sleep Apnea

It is a disorder that affects your breathing. People with sleep apnea have marked reduction in their breathing patterns and they may pause breathing altogether. There are two different types of sleep apnea:

  • Central Sleep Apnea - is where the brain does not send signals to the muscles to breath. 
  • Obstructive Sleep Apnea - is where the brain does send a signal to the muscles to breathe.

What happens is that the person's airways obstructed and prevents the correct amount of air flow to pass. It is possible to suffer from both forms of sleep apnea. Many people with this condition are obese and have to sleep with breathing apparatus during the night.

Restless Leg Syndrome

It is a sleep disorder that makes a person feel uncomfortable sensations in their legs. The person may also have an uncontrollable desire to move their legs. This is not a condition where your legs cramp. A person with this sleep disorder experience strange feelings in their leg such as tingling, pulling, prickly feeling or pins and needles feeling. It is considered as a sleep disorder because person finds difficulty in finding the exact comfortable position of the leg during sleep which leads to sleep disorientation.


It is a disease that affects your central nervous system. This results in you experiencing daytime sleepiness, known as EDS. People who have narcolepsy often have loss of muscular tone, hallucinations, and an inability to move or talk. These symptoms may be present at once or independently and they can be in various forms of severity determining the stage disorder.

Sleep paralysis

It is a terrifying phenomenon where an individual wakes up during REM sleep, to find that their body is effectively paralyzed. This petrifying encounter can last from several seconds to several minutes and is often accompanied by panic attacks and hallucinations. Stress, depression and lack of sleep have all been linked to sleep paralysis but, as there is no clear cause of the condition, there is no guaranteed way to prevent it.

REM Sleep Behaviour Disorder

REM Sleep Behaviour prevents an individual’s muscles from paralyzing during sleep. This means that sufferers will act out their dreams. They can talk, kick and even walk about as though they were awake. In 2008, father-of-two Brian Thomas learned how devastating this disorder can be. Whilst acting out a dream in which he believed he was fighting off intruders, Thomas strangled his wife Christine to death. Due to his history of the condition and numerous character references, Thomas was acquitted of the murder.

Exploding Head Syndrome

It is when individual shear loud imagined noises when they are on the point of falling asleep or waking up. The noises have been described as sounding similar to bombs exploding, cymbals crashing or doors slamming. Some sufferers say they are accompanied by flashes of light or muscle spasms. And the condition is surprisingly common. A study by the European Sleep Research Society found that a staggering 18% of people have experienced it at least once. Exploding Head Syndrome is caused by a sudden burst of neural activity, most probably brought on by sleep disruption, such as jet lag or temporary insomnia.

Kleine Levin Syndrome

Also known as ‘Sleeping Beauty Syndrome’, Kleene-Levin Syndrome mainly affects teenage boys. Sufferers spend up to 23 hours a day asleep, sometimes for many days or weeks in a row. When they are awake, they tend to have heightened hunger and sexual drives. The syndrome occurs over several years, with breaks of a few months in between episodes. Nobody knows what causes the condition, although two-thirds of diagnosed patients suffered from viral infections shortly before their illness began. Whilst there is no definitive cure for Kleine-Levin Syndrome, its symptoms appear to be reduced by the mood stabilizer lithium.


Sleep Related Sleeping Disorder

Most common in middle-aged women, Sleep-Related Eating Disorder generates uncontrollable cravings that make sufferers binge on food during the night time. This is not like conventional mid-night snacking, however, as those affected have no control over their habits and often don’t remember even leaving their beds. Whilst sugary snacks and junk foods are the most popular items of choice, some individuals opt for peculiar concoctions. Sufferers have been known to eat cat food, cigarette butts or salt sandwiches.


In 2014, Mikael Halverson from Sweden had his conviction for the rape of his female roommate overturned when it emerged that he suffered from a sinister disorder called sexennial. Saxonians often engage in sexual activities whilst completely asleep, with no control over what they do or recollection of their actions. Most commonly, this involves masturbation or fondling but - it some cases - it can lead to rape. Dr Kingman Stroh, of the Sleep Center at Case Medical Center in Cleveland said that it is very difficult to fake sexennial, adjudges look at previous medical history, sleep studies and character witnesses to make an assessment.

Nocturnal Death Syndrome

Sudden Unexpected Nocturnal Death Syndrome can occur to anyone, often with little or no prior symptoms. Post-mortems reveal that the majority of victims had previously unknown heart conditions. The syndrome was first noted in the 1970s, amongst members of the Hmong people from Laos. Doctors noticed that apparently healthy Hmong men were dying in their sleep with remarkable frequency. The deaths generated the mythology of ‘datum’ [da-chop], the idea that a jealous hag-like woman would sit on their chests at night and stop them breathing. It is now thought that the Hmong people were so convinced by the idea of dab steam that their overwhelming fear of it triggered their genetic heart defects, causing their deaths

If you think you may be suffering from any of these sleep disorders then consult with your doctor for further advice. 

Effect of Electronic on sleep cycle

The most disturbing things for sleep that we do is the overuse of screen time which includes things like TV, mobile phones, iPads, tablets or any kind of electronic device. These electronic device effect sleep cycle in various way. Some most common impact are:

  • Disturbed sleep cycle routine
  • Melatonin Dysregulation
  • Altered Sleep Waves

Disturbed sleep cycle routine

When you overuse your screen time, so first of all, it delays you from going to bed because you get so involved in your tablets or iPhones or screen time that you become addicted, it raises a chemical in the body called dopamine. This is what keeps you engaged in these devices. So, it's going to delay your time going to bed which result in distortion in the sleep cycle and relatively a smaller number of sleep cycle. it keeps our brain stimulated so this stops you from winding down at night time, which have sever clinical complication.

Melatonin Dysregulation

Screens emits a blue light. Now blue lights mimic daytime and the brain thinks it's daytime. It stops the release of a hormone in our body called melatonin. Melatonin is our sleep hormone and this is absolutely crucial that you have a lot of melatonin at nighttime in the body. It's actually at its highest peak at night time, ready to be released in time to allow you to go asleep and also to stay asleep during the night time. It is because it helps to regulate our sleep cycles during the nighttime and our sleep stages.

Altered Sleep Waves

Device radiation, it is another factor that should not be neglected. On an average, any electronic device radiates a sufficient amount of radiation of very low to very high frequencies that actually interferes with normal brain waves co-called sleep waves. They keep stimulating reticular system of the body also known as “sleep switch of the body” which result in distortion in sleep cycle duration and also cause wakefulness. it can also add to hyperactivity during the daytime.

To ensure better sleep health, use of those electronic devices should be monitored and frequent brake should be taken. These breaks help sensory system and neuron to get relaxed and help the glial cell to remove metabolic waste produced during the use of these electronic devices. Doctors suggest that at once no device should be used more than 30-45 minutes and to maintain such intervals short brakes are mandatory.


Do Sleep App work?

No, sleep app doesn’t work in reality but at least they are useful to get some rough data about sleep pattern and sleep cycle.

They are able to provide a rough idea of how much time you spent in each sleep state but the accuracy is definitely far from perfect. You can't tell when and how much you snore which is useful. The sound paints a picture of how much you toss and turn and rustle in your sheets which provide data that sleep app show.

Those sleep app working with any kind of physical sleep tracker can be more reliable than those sleep app that work alone. Mostly trackers work by using a sensor to monitor movement. An accelerometer is used to measure how fast you move in your sleep, to help determine how a restful you are. The sleep cycle app, in particular, uses your smartphone’s microphone to monitor sound and help determine sleep states and movement which do not provide any significant data to relay on.

In 2016, study showed that those who tracked sleep on their wearable devices started sleeping more hours each night. We could make the assumption that this would also apply to those who use a sleep app.

Though there are things to be considered with these sleep app, for instance as pet jumping on your bed can mess with your data and also they do not measure your heart rate or body temperature like some wearables do which take real-time data during sleep rather than just working on app-based software.

Both wearables and sleep apps do not use EEG technology to measure brainwave patterns like sleep researchers do. Which is one of the most reliable ways to measure which stage of sleep you're in. According to Dr Basal, there's no way of wearables or sleep apps to measure your REM sleep, the smart wakeup functions or sleep apps are meant to wake you up during light states of sleep so you don't feel groggy in the morning.

if you're serious about tracking your sleep with higher accuracy then it is better to use something like a wearables, like Fitness Band or fitness Ring.

Because it measures your hot dynamics pulse strength, body temperature and many more parameter based on the hardware, you get more reliable data than just putting a phone next to your bed and basically crossing your fingers and hoping for the best before you go to sleep.

Popular posts from this blog

Scholarship in Nepal for MBBS 2021 Updated-TU/KU/BPKIHS/PAHS/CEE

In Nepal, there are a total of 356 Scholarship seats for the MBBS program. This is as per the provision for a 75% scholarship in a governmental college. This is a total scholarship provided by TU+KU+BPKIHS+PAHS. These seats include both MOE and individual scholarship offered by the respective college. And altogether there are 516 scholarship seats for MBBS including MBBS seats provided by Embassy and Jagdamba Guthi. For the latest {2021 onward} MBBS seats distribution in different Categories by MEC  CLICK HERE . To have look at result of MBBS 2021 Medical Education Common Entrance Examination {MECEE-BL}  DOWNLOAD HERE.   Here we will discuss the scholarship in Nepal for MBBS and seat distribution in these headings: Scholarships for MBBS- by the individual college Scholarships for MBBS – by MOE Scholarships for MBBS-by different Embassy Scholarships for MBBS- by Jagdamba Guthi Common Entrance Exam Scholarships in Nepal for MBBS- by Individual college Institute of Medicine

Scholarship and Open MBBS seats in Nepal 2022 Updated

In Nepal, there are several autonomous medical institutions and Universities which are conducting MBBS programme.  And there are 1835 Medical MBBS seats in Nepal. It includes all the MBBS seats distributed across the Medical institutions and Universities in Nepal . These MBBS seats are further divided into different categories. These are Paying seats and Scholarship seats.  Scholarship seats include both Reservation and Open scholarship seats, whereas other paying seats include both general paying seats and foreign paying seats.   Introduction In Nepal, the MBBS programme has been started in 1978. In the early period of the MBBS study, there were few medical colleges that were running under the affiliation of foreign medical universities Few were autonomous and few were under universities residing in Nepal. Later on, all the operational medical colleges were brought under the affiliation of universities residing in Nepal or made to run autonomously as an independent medical college.  

MECEE-BL 2022 MBBS-BDS-BASLP-Bsc.Nursing Entrance Result PDF Download & Seats

MECEE-BL 2022 MBBS, BDS, BASLP, BSc.Nursing And BPT  entrance exam results has been published on 06 April 2022, via the official website of the Medical Education Commission. In the year 2022, a total of 8687 students has secured passing mark in MBBS, BDS, Bsc.Nursing, BASLP, B.Perf.Technology. This result has arranged the student in merit order based on percentile. You can download the merit list PDF (MECEE-BL 2022 result) below. How Many Seats Are Available For MBBS, BDS, BAMS BSc.MIT, BSc.MLT And B.Optometry In Nepal? In Nepal, there are 18 Medical colleges including private, governmental, and autonomous medical colleges that offer MBBS, BDS, BAMS, BSc.MIT, BSc.MLT and B.Optometry program. There are 1835 medical seats in the MBBS program, 565 medical seats in BDS, 80 medical seats in BAMS, 71 medical seats in BSc. MIT, 445 medical seats in BSc.MLT, and 67 seats in B. Optometry across the different medical colleges in Nepal . Students are selected for these seats in different colleges