Hypersomnia is characterized by recurrent episodes of excessive daytime sleepiness or prolonged nighttime sleep. Different from feeling tired due to lack of or interrupted sleep at night, persons with hypersomnia are compelled to nap repeatedly during the day, often at inappropriate times such as at work, during a meal, or in conversation. These daytime naps usually provide no relief from symptoms. Patients often have difficulty waking from a long sleep, and may feel disoriented. Other symptoms may include anxiety, increased irritation, decreased energy, restlessness, slow thinking, slow speech, loss of appetite, hallucinations, and memory difficulty. Some patients lose the ability to function in family, social, occupational, or other settings. Hypersomnia may be caused by another sleep disorder (such as narcolepsy or sleep apnea), dysfunction of the autonomic nervous system, or drug or alcohol abuse. In some cases it results from a physical problem, such as a tumor, head trauma, or injury to the central nervous system. Certain medications, or medicine withdrawal, may also cause hypersomnia. Medical conditions including multiple sclerosis, depression, encephalitis, epilepsy, or obesity may contribute to the disorder. Some people appear to have a genetic predisposition to hypersomnia; in others, there is no known cause. Typically, hypersomnia is first recognized in adolescence or young adulthood.