A growing body of research shows that too much sleep can cause a variety of mental disorders, including depression, in large numbers of people. Because sleep causes depression it is referred to as "depressogenic" in the psychological literature. Wakefulness is antidepressogenic. Depressed patients, who are likely to respond to sleep deprivation, characteristically feel worse in the morning and gradually become freer of their symptoms as evening approaches, as the depressant effects of the previous night's sleep wears off through the wakeful hours of the day. In adulthood eight hours of sleep a night is usually too much. Many of us feel better and function better on five to seven hours a night. Often insomnia occurs when you try to get more sleep than your body actually needs.

People who change to a a high-carbohydrate diet also report less time spent sleeping, more restful sleep, and an increase in dream activity.