Klein-Levin syndrome is an extremely rare sleep disorder (effecting approximately 1 person in a million). It is seen as an aftereffect of several different severe viral infections. Its symptoms include hypersomnia, and episodes of hyperphagia (excessive appetite) and hypersexuality. Episodes generally last for approximately a week at a time, sometimes longer and may reoccur for about ten years. There is no known treatment but Lithium has had some positive effects.