Why and how do you have dreams?

Answer 1

Nobody really knows the why, but it seems to be related to learning and emotional regulation. It is known that acetylcholine plays a role in learning. That chemical may be elevated during REM sleep. Sleep seems to help consolidate memories and calm the emotions, and dreaming could very well play a role in that.

Sleep tends to work like this. You gradually drift into alpha brainwaves. Usually, you don't dream during initial alpha level sleep unless you haven't had dreams in a while, perhaps because of sleep deprivation. But you may exerience a phenomenon similar to dreaming before you fall asleep. Then you move into theta brainwaves, and then delta brainwaves. There might be an even deeper set of brainwaves. Then you cycle to alpha mode again, but usually also in REM sleep mode. That is where you do most of your dreaming. Then you cycle back through the different levels of sleep, perhaps four to seven times. Up to 1/4 of your sleep is spent in dreams.