Definition

The phase of sleep that is considered the quiet or restful phase. During the three stages of non-REM sleep, a person falls asleep and then moves from a light sleep into a deep sleep. This is when a person’s brain activity, breathing, and heart rate slow down, body temperature drops, muscles relax, and eye movements stop. Non-REM sleep plays an important role in helping the body repair tissues, build bone and muscle, and strengthen its immune system. During normal sleep, a person goes through four to five sleep cycles that last about 90 minutes each and include both non-REM sleep and REM sleep. Also called non-rapid eye movement sleep and NREM sleep.