Non-rapid eye movement (non-REM) sleep is one of two basic states or phases of sleep. Because it is a time of reduced brain activation, its also referred to as quiet sleep. Non-REM sleep includes stages 1 and 2, which are light sleep, and 3 and 4, which are deep sleep. Quiet sleep contrasts with REM sleep (also called paradoxical sleep) because there is more cognitive activity during REM sleep and it is accompanied by paralysis of the muscles.
In Our Own Words
Quiet sleep, or non-rapid eye movement sleep, is one of two major sleep phases. If you slumber normally, you typically fall asleep less than 15 minutes after retiring and enter non-REM sleep first, moving gradually from light sleep, stage 1, to deep sleep, stage 4. Non-REM sleep is also called quiet sleep because the mind slows down, and blood circulation does too. When you are in non-REM sleep, your heart rate and blood pressure decline. Breathing becomes slower and steady. Your muscles are relaxed, but movements can still occur.
After an hour or less of non-REM sleep, the body shifts to the REM phase. It is so named because the eyes move rapidly in all directions, although the eyelids remain shut. While respirations are slow, the brain ramps up in dream phase of sleep. After another 30 minutes or so, the body transitions back to non-REM, a sleep pattern that continues throughout the night.