It is commonly thought that the body and brain shut down for a few hours each night to rest in preparation for the next day. However, neither the body nor the brain shut down when we sleep. They are actually frequently working even harder than they do during the day, undergoing processes to restore cells, process information, and improve health. The body follows a natural 24 hour rhythm of waking hours and sleep called the circadian rhythm. This rhythm is determined by the hours of light and genetics that control hormone release in the body.