There are several possible causes for excessive sleepiness. Most of them tend to cause disturbances in sleep that often go undetected by the patient: the person thinks they are getting enough sleep, but even though they are in bed they are not sleeping soundly. Possible causes of excessive sleepiness include:
- Primary sleep disorders such as narcolepsy or sleep apnea.
- Dysfunction of the autonomic nervous system.
- Drug or alcohol abuse.
- Brain tumor.
- Head trauma or other central nervous system injury.
- Certain medications, or withdrawal from some medications.
- Medical conditions including multiple sclerosis, depression, encephalitis, epilepsy, or obesity may contribute to the disorder.
- Genetic predisposition to hypersomnia.
- Idiopathic hypersomnia, or excessive sleepiness for which there is no known cause (typically affects adolescents and young adults).
- Kleine-Levin Syndrome, a rare neurological disorder that causes recurrent hypersomnia.
