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Jun 14, 2021
6 min read

The 5 stages of sleep: what they mean

Sleep is so much more complex than just closing your eyes and catching some ZZZs. The sleep cycle is divided into five distinct stages of sleep called Wake, N1, N2, N3, and rapid eye movement (REM) sleep. Each of these stages has its own effects on the body. How you move through these stages can change with age, medical conditions, and medications.

steve silvestro

Reviewed by Steve Silvestro, MD

Written by Ellyn Vohnoutka, BSN, RN

Disclaimer

If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

For many people, sleep seems like a simple concept. You close your eyes, dream a little, and wake up eight hours later feeling refreshed. But for some people, trying to get a good night’s sleep can be a challenge.

Sleep is actually pretty complex, with multiple stages, changing brainwaves, and countless known and unknown functions. Here’s what we know about the stages of sleep, what conditions can affect them, and some tips you can use to get a better night’s sleep.

What is the sleep cycle?

Every night, your body moves through several different levels of sleep. Each level has unique characteristics, including brain wave patterns, eye movements, and muscle tone. Together, these stages are called the sleep cycle (Institute of Medicine, 2006).

Your body’s circadian rhythm controls your sleep cycle. The circadian rhythm is your body’s internal clock, generated by the hypothalamus in your brain.

Besides your sleep cycle, your circadian rhythm also plays a part in regulating the following (Institute of Medicine, 2006): 

  • Physical activity
  • Food consumption
  • Body temperature
  • Heart rate
  • Muscle tone
  • Hormone secretion

Your sleep cycle consists of two different types of sleep, non-rapid eye movement (NREM) sleep and rapid eye movement (REM). NREM is further divided into four distinct stages called Wake, N1, N2, and N3 (Institute of Medicine, 2006).

Your brain cycles through these stages as you sleep. The average length of the first cycle is 70 to 100 minutes, with later cycles taking up to 120 minutes. In most adults, REM sleep increases as the night progresses, and N3 may disappear altogether sometimes (Institute of Medicine, 2006).

What are the stages of sleep?

Researchers uncovered the sleep cycle and its different stages using an electroencephalogram (EEG), a medical device used to trace the electrical patterns of brain activity (Institute of Medicine, 2006). Let’s look at the five stages in a typical sleep cycle. 

1. Wake

The first stage of sleep begins before you even fall asleep. The wake stage is subdivided into two more stages—eyes-open and eyes-closed. During eye-open wakefulness, there are alpha and beta brain waves present. Beta waves are more prominent. As you fall asleep and your eyes close, the alpha waves become more pronounced (Patel, 2021).

2. N1

The N1 stage is a transitional stage. It is the lightest stage of sleep and typically lasts 1–5 minutes. About half of the alpha waves are replaced with another type of wave called low-amplitude mixed-frequency (LAMF) activity during this light sleep stage. Your breathing occurs at a regular rate, and your skeletal muscles (the ones you use to move around) still have some tone. This stage is the beginning of non-REM sleep (Patel, 2021).

3. N2

As you sink into deeper sleep, your heart rate and body temperature drop, signaling the start of the N2 stage of sleep. The N2 stage lasts about 25 minutes in the first sleep cycle and gets longer with each cycle throughout the night (Patel, 2021).

4. N3

Stage N3 is the deepest stage of sleep and is the most difficult to wake up from. It is also called slow-wave sleep for the delta waves shown on EEG. For some people, not even loud noises will wake them from this stage. If you do get woken up, you will likely feel mentally foggy. Studies have shown moderate impairments on cognitive testing for 30 minutes to an hour for people waking directly from deep N3 sleep (Patel, 2021).

During this stage, your body will (Patel, 2021):

  • Repair and regrow tissue
  • Build muscle and bone
  • Strengthen the immune system

Researchers are currently studying ways to enhance cognitive ability by stimulating the brain during slow-wave sleep with various types of sound, electricity, and medications. More study is needed, but stimulation has improved performance in several cognitive domains (Zhang, 2019).

5. REM sleep

REM sleep is the stage associated with dreaming. During this stage, your breathing rate becomes less regular. The skeletal muscles are relaxed and unmoving except for the eyes and diaphragm. Surprisingly, during this stage, your EEG would look very similar to an awake person’s. REM starts about 90 minutes after falling asleep and gets longer throughout the night (Patel, 2021).

Researchers met the first descriptions of REM sleep with skepticism. We now understand how essential REM sleep is to the function of the brain. However, though there are many theories, we still don’t quite know the function of REM or how and why we dream (Peever, 2017).

Humans aren’t the only species that experience REM sleep. All land-dwelling mammals, birds, reptiles, and some aquatic invertebrates also go through a REM stage. New data suggests that REM sleep may help facilitate learning and memory in most of the animal kingdom, humans included, by regulating activity in the gaps between the neurons in the brain (Peever, 2017). 

What affects the stages of sleep?

Of course, these stages of sleep don’t always work the way they’re supposed to. When that happens, some people may develop insomnia or other sleep disorders. Many things can impact the stages of sleep.

Medical conditions

Many medical conditions can affect your sleep cycles. These include (Karna, 2021):

  • Heart conditions, such as heart failure
  • Neurologic conditions, such as central sleep apnea, restless leg disorder, or degenerative disorders
  • Endocrine conditions, such as hyperthyroidism, pregnancy, or diabetes
  • Pulmonary conditions, such as obstructive sleep apnea, asthma, or chronic obstructive pulmonary disease (COPD)
  • Gastrointestinal disorders, such as acid reflux
  • Musculoskeletal conditions, such as arthritis pain, fibromyalgia, or any chronic pain

Mental health

Mental health conditions and medications can also cause changes to how your body moves through the stages of sleep (Karna, 2021):

  • Depression can cause difficulty falling asleep, waking up in the middle of the night, decreased slow-wave sleep, less time to get into REM, and increased REM intensity.
  • Anxiety disorders may cause trouble falling asleep, staying asleep, and not feeling rested after sleep.
  • Post-traumatic stress disorder (PTSD) can produce vivid and terrifying nightmares.
  • Antidepressants may interfere with your normal REM sleep patterns.
  • Benzodiazepines may cause rebound insomnia after stopping the medication, especially in older adults.

Age

Age also plays a part in changing your sleep cycles, including (Li, 2018):

  • Falling asleep earlier
  • Shortened sleep duration
  • More frequent daytime naps
  • More frequent awakenings at night
  • Less slow-wave sleep

Sleep changes are a normal part of aging. Most of these changes actually occur during young and middle adulthood. Changes in the circadian system and the amount and pattern of sleep-related hormone secretion contribute to age-related changes in sleep (Li, 2018).

How to encourage better sleep

Sleep is receiving increasing attention, as there is growing evidence that poor sleep is associated with adverse health outcomes, including cognitive declines in older adults (Li, 2018).

Most adults require 7–8 hours of sleep each night. Children and teenagers need more. Older adults may sleep less at night but may still need to make up the rest of the time with daytime naps (U.S. National Library of Medicine, n.d.).

There are some ways to improve your sleep at night if you are struggling.

Calm your stress

Calming your mind can make it easier for you to fall asleep. You can try writing down anything bothering you in a journal, learning relaxation techniques, or finding other calming activities to do two hours before bedtime (U.S. National Library of Medicine, n.d.).

Change your activities

Try to be more active during the daytime and avoid naps to make it more likely that you will be tired at bedtime. It would help if you also cut back on caffeine, nicotine, and alcohol. A sleep routine can help signal your mind and body that it’s time to wind down for bed (U.S. National Library of Medicine, n.d.).

Don’t stare at the ceiling

You can’t force yourself to fall asleep; this will just leave you frustrated. If you can’t fall asleep within 30 minutes, move to another room and try a quiet activity until you feel sleepy. If that doesn’t work right away, keep trying before getting back into bed (U.S. National Library of Medicine, n.d.).

When to talk to your healthcare provider

If any of the following are keeping you up at night, talk with a healthcare provider (U.S. National Library of Medicine, n.d.):

  • You feel sad or depressed.
  • Pain or discomfort is keeping you awake.
  • You think medicine or supplements may be keeping you awake.
  • You have been using sleep medicines without talking to your provider first.

References

  1. Institute of Medicine (US) Committee on Sleep Medicine and Research; Colten, H. R., & Altevogt, B. M. (Eds.). (2006). Sleep disorders and sleep deprivation: an unmet public health problem. Sleep Physiology. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK19956/ 
  2. Karna B, Gupta V. (2021). Sleep disorder. [Updated 2021 Feb 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK560720/ 
  3. Li, J., Vitiello, M. V., & Gooneratne, N. S. (2018). Sleep in normal aging. Sleep Medicine Clinics, 13(1), 1–11. doi: 10.1016/j.jsmc.2017.09.001. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5841578/ 
  4. Peever, J., & Fuller, P. M. (2017). The biology of REM sleep. Current biology: CB, 27(22), R1237–R1248. doi: 10.1016/j.cub.2017.10.026. Retrieved from https://pubmed.ncbi.nlm.nih.gov/29161567/ 
  5. Patel AK, Reddy V, Araujo JF. (2021). Physiology, sleep stages. [Updated 2021 Apr 22]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK526132 
  6. U.S. National Library of Medicine. (n.d.). Changing your sleep habits: MedlinePlus Medical Encyclopedia. MedlinePlus. Retrieved from https://medlineplus.gov/ency/patientinstructions/000757.htm 
  7. Zhang, Y., & Gruber, R. (2019). Can slow-wave sleep enhancement improve memory? A review of current approaches and cognitive outcomes. The Yale Journal of Biology and Medicine, 92(1), 63–80. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6430170/