In full: non-rapid eye movement sleep (Show more) Also called: non-REM sleep (Show more) NREM sleep, one of two phases in the sleep cycle, considered the restful or quiet sleep phase. The other phase of the human sleep cycle is known as rapid eye movement (REM) sleep. A single sleep cycle, with both NREM and REM phases, lasts about 90 to 110 minutes; most adults complete the cycle four to six times per night. NREM sleep is conventionally subdivided into three stages—N1, N2, and N3—based on electroencephalography (EEG) criteria. N1 is a transitional stage, typically lasting one to seven minutes, as brain activity settles from wakefulness to sleep. This is represented electrically in the ...(100 of 651 words) Access the full article Help support true facts by becoming a member. Subscribe today!