Describe the human sleep cycle, including the four stages and REM sleep, and what happens in each

Stage 1 is the beginning of the sleep cycle and is a relatively light stage of sleep. Stage 1 can be considered a transition period between wakefulness and sleep. Stage 2 is the second stage of sleep and lasts for approximately 20 minutes. During stage 2 sleep, You become less aware of your surroundings.Body temperature drops. Breathing and heart rate become more regular. During stage 3 sleep: Muscles relax. Blood pressure and breathing rate drop. Deepest sleep occurs. During REM sleep: The brain becomes more active.
The body becomes relaxed and immobilized. Dreams occur. Eyes move rapidly.