Non-REM Sleep (NREM)

There are two main categories of sleep, Non-Rapid Eye Movement or Non-REM (NREM) and Rapid Eye Movement (REM). NREM sleep contains all stages of sleep except REM (there are 5, although many debate this, instead saying there are 4 stages of sleep).

Non-REM sleep contains light stages of sleep (stage 1), to full sleep (Stage 2), and deep or slow wave sleep (stages 3 and 4).