High Quality Content by WIKIPEDIA articles! Slow-wave sleep (SWS), often referred to as deep sleep, consists of stages 3 and 4 of non-rapid eye movement sleep, according to the Rechtschaffen Kales (R K) standard of 1968. As of 2008, the American Academy of Sleep Medicine (AASM) has discontinued the use of stage 4, such that the previous stages 3 and 4 now are combined as stage 3. An epoch (30 seconds of sleep) which consists of 20% or more slow wave (delta) sleep, now is considered to be stage 3.