This article is from the Dreaming FAQ, by "Lars Rune Foleide" email@example.com .
Dreaming is highly involved in learning and memory. If you have a bad
experience, it will be digested in your dream. Most likely in a
nightmare. Dreams are quite often a reflection of your day memory. The
protein-synthesis is highly active during REM, so if you want to
learn, then staying in REM is a good move. REM is also necessary to
supply the cornea with oxygen. Delta sleep, associated with large,
slow brain waves, is what most people call the deepest kind of sleep,
when you are hardest to awaken. It is necessary for the brain/body to
rest and heal. A good balance between delta sleep and REM is important
for learning. Growth hormones are also produced during delta sleep.