Learn about the sleep health app

The Importance of Sleep - Understanding the Sleep Stages

By: Tracy R. Nasca and Rochelle Goldberg, M.D.

How much sleep do we need and why is sleep important?  Most doctors would tell us that the amount of sleep one needs varies from person to person.  We should feel refreshed and alert upon awakening and not need a day time nap to get us through the day. Sleep needs change from birth to old age.  The general thought is that newborns through the first year need up to 18 hours daily, 1-3 year olds need 12-15, ages 3-5 need 11-13 hours, 2-12 year olds need 9-11, and teens need 9-10 hours.   Adult sleep needs (beginning around 17 years old through the elderly) are generally 7- 8 hours.

Sleep is something most of us take for granted, yet, it is as important to life and health as the air we breathe.  When we don’t get enough sleep, we suffer in a multitude of ways.  Sleep deprivation causes cognitive loss such as memory, concentration, moodiness, as well as hyperactivity in children.  It also can result in health problems including obesity heart disease, hypertension and diabetes.  It may also increase the risk of injury, such as motor vehicle crashes.

Sleep Stages are as follows:

Stage W (Wakefulness)

Stage N1 (NREM 1)

Stage N2 (NREM 2)

Stage N3 (NREM 3)

Stage R (REM)

(NREM = Non REM sleep)

During the course of an eight hour sleep period, a healthy sleeper should cycle through the various sleep stages every 90 minutes or so.

Stage N1 (NREM1) sleep is a transition period from being awake to falling asleep.  During this time you may have a sudden dream onset.  You are drifting off to sleep and may still feel aware of your surroundings and easily be aroused back to wakefulness.

From Stage N1, you will enter Stage N2 where your breathing and heart rate will begin to slow.  During the continuous sleep cycles throughout the night, we should spend about half of our sleep time in Stage N2.

Next comes Stage N3, sometimes referred to as Delta Sleep or slow wave sleep, because of the slow delta brain waves, which have been recorded during this sleep stage.  N3 sleep is a regenerative period where your body heals and repairs itself.  The first episode of Stage N3 lasts from 45-90 minutes.  Subsequent episodes of N3 sleep have shorter and shorter time periods as the night progresses. 

N3 sleep decreases with age such that elderly people may have no measured N3 sleep at night.  This occurs in healthy sleepers and does not indicate a disorder or disease state in itself. 

Stage R is referred to as REM sleep or “rapid eye movement” sleep.  The first REM sleep episode generally occurs after 90-110 minutes of sleep, cycling about every 90 minutes thereafter.  REM sleep periods tend to be longer later in the night.  Our heart and breathing rates increase and become irregular.  It is during REM sleep that we dream.  Many of us will remember dreams from the REM stage.  The body creates chemicals that render us temporarily paralyzed so that we do not act out our dreams. . In this stage, the brain is extremely active, and our eyes, although closed, dart back and forth as if we were awake.

During the diagnostic overnight sleep study or Polysomnogram, our sleep architecture is tracked and recorded.  With over 80 different sleep disorders, often our diagnoses are partially determined by how we cycle through these sleep stages.  As an example, people with narcolepsy fall directly in to REM sleep.  People with apnea may have reduced stages N3 and REM when their interrupted breathing causes sleep to be fragmented, possibly alternating between stages N1 and N2 over and over all night.

Understanding the sleep stages, how one should cycle through them and the necessity of achieving healthy sleep hours, is important information for us patients to understand as we strive to become more knowledgeable about our own sleep health.

The information included on this site is for educational purposes only. It is not intended nor implied to be a substitute for professional medical advice. Contact your physician or health care provider when you have health related questions. Never disregard or delay medical advice because of information you have obtained on this site.