Sleep cycle

The sleep cycle is an oscillation between the slow-wave and REM (paradoxical) phases of sleep, sometimes called the ultradian sleep cycle, sleep–dream cycle, or REM-NREM cycle, to distinguish it from the circadian alternation between sleep and wakefulness. In humans this cycle takes 1–2 hours.



Stage 1 (light sleep) – Stage 2 (light sleep) – Stage 3 (deep sleep) – Stage 2 (light sleep) – Stage 1 (light sleep) – REM Sleep

WAKING	REM SLEEP	NREM SLEEP
Stage 0	Stage R	LIGHT SLEEP DEEP SLEEP STAGE 1 STAGE 2 STAGE 3 STAGE 4
Eyes open, responsive to external stimuli, can hold intelligible conversation	Brain waves similar to waking. Most vivid dreams happen in this stage. Body does not move.	TRANSITION BETWEEN WAKING AND SLEEP. IF AWAKENED, PERSON WILL CLAIM WAS NEVER ASLEEP. MAIN BODY OF LIGHT SLEEP. MEMORY CONSOLIDATION. SYNAPTIC PRUNING. SLOW WAVES ON EEG READINGS. SLOW WAVES ON EEG READINGS.
16 to 18 hours per day	90 to 120 min/night	4 to 7 hours per night