Definition

The phase of sleep that is considered the quiet or restful phase. During the three stages of NREM 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. NREM 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 NREM sleep and REM sleep. Also called non-rapid eye movement sleep and non-REM sleep.