Stage 3 non-REM sleep, also known as slow-wave sleep (SWS), is the deepest stage of sleep, and is the third of the three stages of non-REM sleep. In this stage of sleep we transition from the slow theta brainwaves of N2 to even slower and bigger delta waves; this is where stage 3’s alternate name of “slow-wave sleep” comes from. In this stage of sleep your eyes don’t move, your muscles don’t move: you’re deep, deep in slumber. If you’re disturbed in this stage of sleep, chances are you won’t wake up. If someone does manage to rouse you out of this stage of sleep, you will probably suffer from “sleep inertia”, which is to say you will feel very sleepy and groggy, and probably really not very pleased about being woken up. This is the stage of sleep that’s least associated with dream content; however, whether this is due to a genuine lack of content, or to sleep inertia, remains unknown. To see where in the night this stage of sleep occurs, take a look at a typical hypnogram. The fantastic diagram below from the website HumanPhysiology.Academy illustrates what our brainwaves look like in the different stages of sleep. In this diagram, SWS is referred to as “Delta Sleep”.
