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Deep Sleep – Basics You Need To Know

The information on this website is not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice. Read our full medical disclaimer.

Deep sleep is one of the Non-REM stages of our sleep and is critical to your health and well-being. Although we are aware of some of the physiological and psychological benefits, as well as the negative impact of deep sleep deprivation, there is still a lot we don’t know abou the effects of deep sleep.


Deep sleep is immensely important for memory consolidation and tissue regeneration. Unfortunately, the amount of deep sleep we get declines as we age. Obtaining deep sleep can be prevented by numerous factors including drug use, alcohol, stress, and sleep-related disorders.

This doesn’t mean we have to go through life deep-sleep deprived – we just have to tune into our natural biorhythm and take care of our health by monitoring the amount of sleep we get and by improving our sleep quality.

What part of sleep is deep sleep?

Our sleep cycle is typically divided into four stages. These are – Stage 1 and Stage 2, which fall into the category of light sleep, followed by Stage 3, which falls into the category of deep sleep, and finally REM (rapid eye movement) sleep. The first three stages together make up the Non-REM sleep – as opposed to REM sleep – and are consecutively labeled as N1, N2, and N3.

Deep sleep is also known as slow-wave sleep (SWS) and delta sleep due to the types of brain waves produced during this stage of the sleep cycle. Low-frequency delta waves characterize the N3 stage.

Are there four or five sleep stages?

There are four sleep stages. They used to be labeled a bit differently in the past when compared to modern usage. Deep sleep was considered to consist of two stages – 3 and 4. This division was made due to the frequency of delta wave occurrence – Stage 3 consisted of a low amount of delta waves whereas they were more frequent in Stage 4. This led scientists to conclude that Stage 4 meant that the person had reached a deeper level of sleep. However, since 2008 the American Academy of Sleep Medicine refers to both of these as Stage 3 since there wasn’t any clear evidence that there were two distinct stages of deep sleep.

When does deep sleep occur and how long does it last?

Deep sleep begins at approximately the 45th minute after falling asleep, that is, after our brain has cycled through Stages 1 and 2. It lasts significantly longer in the first half of the night than in the second. We obtain the most of our nightly deep sleep in the first two sleep cycles.

A healthy adult spends about 20% of their time in deep sleep per night. The percent of the deep sleep we get depends on our age, sex, health, lifestyle and sleeping habits.

What happens during deep sleep?

There are physical, psychological and physiological processes in our body which occur during deep sleep:

  • The release of growth hormone (GH), which helps your body grow and develop when young and is still important in older ages for cell restoration and rejuvenation and tissue reparation
  • Memory consolidation and transfer from short-term into long-term memory
  • No response to external stimuli – a person may be very difficult to wake up from deep sleep; if woken, they may be disoriented and feel sluggish
  • The immune system is boosted.
  • Muscles are relaxed, no eye movement.
  • Breathing slows down and heart rate and body temperature drop.
  • Energy is restored for the following day.
  • The following parasomnias occur – bedwetting, sleepwalking, night terrors.
  • Glucose levels in the brain increase.
  • Decreased metabolism allows oxygen byproducts to clear our of the brain.

What are the benefits of deep sleep?

Here are some of the positive aspects of getting enough deep sleep:

  • Feeling well-rested. After getting enough deep sleep, you should feel no need to sleep again any time soon. It’s important to note that if you take a daytime nap long enough to reach deep sleep, your overall sleep propensity will decrease and you might end up going to bed very late.
  • Your mind is refreshed and you will be able to learn new things easily.
  • The tissues in your body are repaired and cells are restored. This is very important especially if your body is fighting a disease or an illness.
  • The brain is cleared of plaque buildup.

Deep sleep and age

Slow-wave sleep decreases as we age. A study notes that the amount of delta sleep is associated with growth hormone and age in men. It found that the amount of delta sleep in young individuals (16-25 years of age) decreased from about 20% to 3.4% in mid-life (36-50 years old).

Since it’s associated with the release of growth hormone, deep sleep seems to be an indicator of youth.

Disorders linked to deep sleep

There are some sleep disorders (parasomnias) which typically occur during the N3 stage of sleep. They are also called Non-rapid eye movement sleep arousal disorders because a person is partially awake – enough to perform complex activities, but not enough to be considered fully awake. Bedwetting is not a sleep arousal disorder.

  • Sleepwalking (somnambulism). Although more common in children; sleepwalking occurs with adults, too. It may be an indicator of sleep deprivation, intoxication, or medications. Good sleep hygiene often eliminates this problem.
  • Night terrors or sleep terrors. During a night terror episode, people may seem awake as they express inconsolable panic, scream, hit or try to escape.
  • Bedwetting (nocturnal enuresis). Mostly happens in children before the age of 7. It should not be considered a problem until this age. Bedwetting is mainly a sign of immaturity and stops when children learn how to control their bladder.
  • Sleep sex (sexsomnia). This should not be confused with erotic dreams. Sexsomnia is an unusual behavior in which a person engages in sex acts while sleeping.
  • Sleepwalking, night terrors and bedwetting happen more frequently in those who suffer from sleep apnea. Bedwetting is usually accompanied with sleepwalking and even night terrors. These disorders tend to run in families.

How to get enough deep sleep

In general, when someone refers to getting “a good night’s sleep” they are talking about getting more deep sleep. You should go to bed before midnight if you want to get more deep, restorative sleep. However, an interesting phenomenon has been reported – not only do we get more deep sleep in the first couple of hours after falling asleep, but we also get more deep sleep early in the night. If you go to sleep at 11 pm, you will get more deep sleep and more REM sleep. If you go to sleep at 3 am, you are likely to get more REM sleep only without the corresponding increase in deep sleep.

Make sure to follow all of the standard sleep hygiene rules, including these:  

  • Respect your circadian rhythm. Get plenty of sleep every night by keeping a regular sleep schedule.
  • Avoid alcohol and nicotine. Don’t drink any alcohol to ensure that you get your delta sleep.
  • Seek help for sleep disorders. People who suffer from obstructive sleep apnea stop breathing several times a night, which causes frequent waking and disrupts the normal sleep cycle. The more you wake up, the less deep sleep you get. Using a CPAP machine to treat sleep apnea may help.
  • Avoid nightly waking. Make your sleep environment calm and quiet. Turn your phone off and don’t drink liquids which may cause frequent toilet visits.
  • Relax. Avoiding stress can positively affect your sleep – especially reaching deeper stages of it.
  • Exercise for at least 30 minutes every day. Working out is believed to promote deep sleep because, after strenuous exercise, the body has to release growth hormone to support muscle growth.

After learning about its benefits, many people wonder how to increase deep sleep. Although it’s important to stick to habits which promote a good night’s rest, there are some other ways to increase deep sleep. One is the drug called gamma hydroxybutyrate (GHB), used by bodybuilders in the past because it supports muscle growth. After being misused as a ‘date rape drug’, it became illegal for over-the-counter consumption and is now used for treating narcolepsy and cataplexy.

Some researchers have discovered that playing certain soundwaves to sleeping individuals resulted in their brain responding by emitting low-frequency delta waves. Certain sounds made people reach deeper stages of sleep when compared with others.

What is deep sleep rebound?

After a period of slow-wave sleep deprivation, the following night the brain will experience more SWS, thus making up for the lost deep sleep. A similar and more well-known phenomenon is REM sleep rebound in which a similar thing happens – the brain ‘hurries up’ to cycle through other stages to reach REM.

What are the differences between REM sleep and deep sleep?

Although people frequently mistake one for the other, REM and deep sleep are not the same. This table shows the main differences (and similarities) between these two stages of sleep.


Non-rapid eye movement stage 3 sleep

Rapid eye movement sleep

Other names

Deep sleep, N3, stage 3, delta sleep, slow-wave sleep (SWS), orthodox sleep, synchronized sleep, (previously also stage 4)

REM, REMS, paradoxical sleep, desynchronized sleep, stage 4 (previously stage 5)

Occurs after stage

Stage 2 (N1, N2, N3)

Stage 2 (N1, N2, N3, N2, REM)

Occurs (minutes after falling asleep)

35-45 minutes

75-90 minutes

The longest periods of this stage happen

In the first half of the night

In the second half of the night



Faster than other sleep stages

Heart rate and breathing

Steady, slow

Inconsistent, fast

Body temperature



Body movement

Muscles relaxed, normally no movement

Muscles are paralyzed (muscle atonia), eyes move rapidly from side to side


May occur, not vivid

Very vivid dreams


Memory consolidation, good memory


body cell and tissue restoration, boosting of immune system

Memory consolidation, good memory


Better ability to read other people’s emotions, high emotional response to stress

Parasomnias, sleep disorders

Bedwetting, night terrors, sleepwalking, sexsomnia

REM sleep behavior disorder (RBD), narcolepsy, sleep paralysis

Deprivation from this particular stage may cause

Insulin resistance, low learning capacity, higher risk of Alzheimer’s


slow physical response, immune system weakening

Insulin resistance, low learning capacity, higher risk of Alzheimer’s


irritability, reduced coping mechanisms, migraines, higher risk of anxiety

Response to external stimuli

No response – a person is completely unaware of their surroundings, almost impossible to wake up

Dreams may depend on external stimuli, a person is easily woken up

After being abruptly woken up from this stage

A person is disoriented, not able to focus

A person reports being woken up from a dream

Additional Resources

  1. The Four Stages Of Sleep And Sleep Cycles. Sleepline. December 8, 2018. https://www.sleepline.com/stages/  Accessed December 11, 2018.
  2. Cline J. The Mysterious Benefits of Deep Sleep. Psychology Today. Posted on October 11, 2010. https://www.psychologytoday.com/us/blog/sleepless-in-america/201010/the-mysterious-benefits-deep-sleep Accessed on December 11, 2018
  3. Cauter E, Leproult R, Plat L. Age-Related Changes in Slow Wave Sleep and REM Sleep and Relationship With Growth Hormone and Cortisol Levels in Healthy Men. August 16, 2000. https://jamanetwork.com/journals/jama/fullarticle/192981 Accessed December 11, 2018.
  4. Dijk D.J. Slow-wave sleep, diabetes, and the sympathetic nervous system. January 29, 2008. https://www.pnas.org/content/105/4/1107 Accessed December 11, 2018.
  5. REM Sleep – How It Works and What The Benefits Are. Sleepline. December 8, 2018. https://www.sleepline.com/rem-sleep/ Accessed December 11, 2018.
  6. Hsu C, Hung H, Tsai L, Hsieh S. The Effect Of Slow Wave Sleep Deprivation On Error Monitoring. Sleep. April 28, 2017. https://academic.oup.com/sleep/article/40/suppl_1/A92/3781469 Accessed December 11, 2018.
  7. Sleep Deprivation – How Losing Sleep Can Ruin Your Health. Sleepline. https://www.sleepline.com/sleep-deprivation/ Posted on November 14, 2018. Accessed on December 11, 2018.
  8. How to Get More Deep Sleep. Sleepline. November 16, 2018. https://www.sleepline.com/how-to-get-more-deep-sleep/ Accessed on December 11, 2018
  9. Gordon, A.M. Your Sleep Cycle Revealed. Psychology today. July 26, 2013.
    https://www.psychologytoday.com/us/blog/between-you-and-me/201307/your-sleep-cycle-revealed Accessed on December 11, 2018
  10. Dan Gartenberg. The brain benefits of deep sleep — and how to get more of it. TED Residency. https://www.ted.com/talks/dan_gartenberg_the_brain_benefits_of_deep_sleep_and_how_to_get_more_of_it/transcript?language=en Accessed on December 11, 2018
  11. Khalighi S, Pires G, et al. Automatic Sleep Staging: A Computer-Assisted Approach for Optimal
    Combination of Features and Polysomnographic Channels. Expert Systems with Applications. December 2013. doi: 10.1016/j.eswa.2013.06.023
  12.  Ferrara M, De Gennaro L, Bertini M. Selective slow-wave sleep (SWS) deprivation and SWS rebound: do we need a fixed SWS amount per night?. Sleep Research Online. 1999;2(1):15-9. https://www.ncbi.nlm.nih.gov/pubmed/11382878 Accessed on December 11, 2018

The information on this website is not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice. Read our full medical disclaimer.

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