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Hypersomnia is a sleep disorder that causes people to feel extremely sleepy throughout the day, regardless of how many hours of sleep they had the night before. Patients with hypersomnia also often sleep for long periods at night and have difficulty waking up in the morning. They may have deep urges to nap repeatedly during the day.

Patients with hypersomnia experience excessive sleepiness, despite typically sleeping at least 25 percent longer than normal. No matter how much sleep they get, patients with hypersomnia rarely feel completely rested. The overwhelming urge to nap can become dangerous when patients are involved in activities that require detailed attention, such as driving.

People with hypersomnia also may have difficulty waking in the morning, which can cause occupational problems, such as frequently being late for work. Excessive sleepiness can impair a person’s ability to concentrate and may affect relationships with others. Some patients begin to engage in automatic behavior. For example, patients may find they have driven long distances before realizing it. Patients are often unable to recall the activity that lead up to the circumstances in which they find themselves.

There are two main categories of hypersomnia: primary and secondary. Primary hypersomnia is hypersomnia that does not have a known cause. The two major forms are idiopathic hypersomnia and recurrent insomnia. Most patients with primary hypersomnia experience chronic sleepiness. However, some patients may experience sleepiness that lasts for days or weeks before resolving, a pattern that may recur over a period of years. Recurrent primary hypersomnia, an uncommon condition also known as Kleine-Levin syndrome, is also characterized by hypersexuality and compulsive eating.

Secondary hypersomnia is hypersomnia that occurs as the result of known factors such as medical conditions (e.g., narcolepsy), physical injury or the use of certain medications (e.g., tranquilizers).

Patients with hypersomnia are at risk of developing related disorders. For example, the social and occupational consequences of hypersomnia may trigger bouts of depression. Patients who take stimulants to remain awake may develop substance abuse disorders.

Hypersomnia is considered to be a less common sleep disorder than insomnia, which involves difficulty falling asleep or staying asleep. Hypersomnia is most likely to first occur in people during adolescence and young adulthood. Some patients may find that their symptoms resolve during middle age.