Stages of sleep

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Stages of sleep

Sleep stages are divided into non–rapid eye movement (non-REM) and rapid eye movement (REM).

Non-REM sleep

Non–rapid eye movement (non-REM) sleep has four stages:

Stages 1 and 2 are light sleep in which breathing is slower than when a person is awake.
Stages 3 and 4 are called slow-wave (delta) sleep, in which the person's rate of breathing slows down further.

REM sleep

Rapid eye movement sleep is deeper than non-REM sleep. During REM sleep:

The eyes and eyelids flutter.
Breathing becomes irregular. During REM sleep, it is normal to have short episodes when breathing stops (apnea).

During sleep, a person usually progresses through the four stages of non-REM sleep before entering REM sleep. This takes about 60 to 90 minutes after falling asleep. The cycle is repeated three to four times each night with more time spent in the REM sleep stage and less time in sleep stages 3 and 4.

Credits

Author	Maria G. Essig, MS, ELS
Editor	Susan Van Houten, RN, BSN, MBA
Associate Editor	Tracy Landauer
Associate Editor	Pat Truman
Primary Medical Reviewer	Caroline S. Rhoads, MD - Internal Medicine
Specialist Medical Reviewer	Jan Ulfberg, MD, PhD - Sleep Disorders
Last Updated	July 13, 2007

Last updated:	July 13, 2007
Author:	Maria G. Essig, MS, ELS
Reviewed By:	Caroline S. Rhoads, MD - Internal Medicine, Jan Ulfberg, MD, PhD - Sleep Disorders
Editors:	Susan Van Houten, RN, BSN, MBA, Pat Truman

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