Sleep is governed by complex molecular and electrical activity in the brain. Sleep onset occurs as the brain responds to accumulated sleep pressure and  the circadian rhythm, with a drop in body temperature helping to initiate sleep onset. Throughout the night, sleep cycles through distinct stages—from light sleep (N1) to deeper sleep (N2 and N3) and finally REM sleep—each serving unique restorative functions. During these stages, the brain processes memories, produces dreams, and clears waste products. Unlike sleep, anesthesia induces an artificial suppression of brain activity, lacking the dynamic patterns and natural transitions seen in sleep. The brain also generates different types of dreams during various sleep stages, with REM sleep producing the most vivid and emotionally intense experiences.