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. Hypersomnia typically affects adolescents and young adults, although the most common causes of the condition for the two age cohorts differ.
This introduction is from the National Institute of Neurological Disorders and Strokes website.
An adult is considered to have hypersomnia if he or she sleeps more than 10 hours per day on a regular basis for at least two weeks.
People who are overweight may be more likely to suffer from hypersomnia. This can often exacerbate weight problems as excessive sleeping decreases metabolic energy consumption, making weight loss more difficult.
Another possible cause is an infection of mononucleosis, as several instances of hypersomnia have been found to arise immediately after such an infection (Dr. Givan, MD, Riley Hospital).
In some instances, the cause of the hypersomnia cannot be determined; in these cases, it is considered to be idiopathic hypersomnia.