Hypersomnia disorders involve excessive daytime sleepiness or the inability to stay awake during the day. People with a hypersomnia disorder typically sleep more than 9 hours in a 24-hour period, and the cause of their sleepiness can’t be attributed to disturbed nighttime sleep or a circadian rhythm problem. The main symptom of hypersomnia is daytime sleepiness, which most people experience from time to time. Nearly half of all adults will have symptoms of a hypersomnia disorder at some point.

What causes hypersomnia?

Hypersomnia that does not appear to be caused by another medical condition or a medication is referred to as primary hypersomnia. Secondary hypersomnias result from other disorders or medications and include:

  • Hypersomnia due to a medical disorder
  • Hypersomnia due to a medication or substance
  • Hypersomnia associated with a psychiatric disorder

Conditions that contribute to daytime sleepiness can increase the risk of a hypersomnia disorder including Low thyroid function, certain brain conditions, kidney conditions, untreated sleep apnea, and depression. Shift work is linked to an increased risk of hypersomnia.


Sleep specialists use several methods, or a combination of methods, to diagnose hypersomnia. You may be asked to keep a sleep diary or take a multiple sleep latency test, a monitored nap during which your sleep is measured. A polysomnogram, or overnight sleep study measuring heart rate, breathing and brain activity during sleep, might also be used in your diagnosis.


This group of disorders includes narcolepsy, a serious condition affecting an individual’s safety and quality of life. However, some hypersomnias are less severe.