Glossary of Sleep-related terms

Sleep Stage 3 (NREM Stage 3)

A stage of NREM sleep defined by at least 20% and not more than 50% of the period consisting of EEG waves of 2 cps or slower, with amplitudes of more than 75 mV (high-amplitude delta waves). It constitutes "deep" NREM sleep, or, so-called slow wave sleep (SWS), and is often combined with stage 4 NREM sleep because of the lack of documented physiological differences between the two. It normally appears usually only in the first third of the sleep episode, and usually compromises 4-6% of total sleep time.1