Non-REM sleep is all sleep that is not REM sleep, and comprises three distinct stages: Stage 1 (sleep onset), Stage 2 (N2), and Stage 3 (SWS). Non-REM sleep typically dominates the first half of a night’s sleep, and with REM typically dominating the second half of a night’s sleep. To see where in the night this stage of sleep occurs, take a look at a typical hypnogram.
