Kleine Levin syndrome is a rare disorder characterized by recurrent episodes of excessive sleep (hypersomnia) along with cognitive and behavioral changes. Affected individuals may sleep for up to 20 hours per day during an episode. These episodes usually last for a few days to a few weeks. An episode may start abruptly and is sometimes preceded by an upper-respiratory-type infection. During an episode, people with Kleine Levin syndrome can also display abnormal behavior, such as excessive food intake (hyperphagia), irritability, childishness, disorientation, hallucinations, and an abnormally uninhibited sex drive. Affected individuals are symptom-free between episodes. The time between episodes varies. Kleine Levin syndrome primarily affects adolescent males, but it also affects females and individuals of other ages. The underlying cause of this condition is unknown. Episodes tend to decrease with advancing age. There are no consistently effective therapies, although stimulants (modafinil, methylphenidate, amphetamine) and mood stabilizers (lithium) may be prescribed with varying results.