F51: Nonorganic sleep disorders

F51.8: Other nonorganic sleep disorders

There are different reasons why we sleep. The reasons have not been fully understood. So far we know, for example, that sleep helps the body to recover. Sleep also develops the memory, and it brings feelings into equilibrium. Sleep has a particular sequence. There are deep sleep phases and lighter sleep phases. These phases alternate during sleep. The sleep-wake cycle is controlled by different influences such as messenger substances in the body. These messenger substances can be influenced by activity and light.