The exact cause of hypersomnia is not clear.
It is thought that problems in the hypothalamus could be behind hypersomnia, though more evidence is required to conclusively prove this connection.
Some evidence point towards the malfunctioning of a chemical, nor - epinephrine, a neurotransmitter, in the case of idiopathic hypersomnia. Although a genetic basis for idiopathic hypersomnia has been suggested, the mode of inheritance has not been determined.
Recently, very low concentrations of chemicals known as hypocretin-1 and hypocretin-2 in the cerebro - spinal fluid were found in primary hypersomnia patients.
Excessive Sleepiness is reported to be caused by the following factors:
- Sleep deprivation: Here a person voluntarily deprives himself of sleep. This is the commonest cause of daytime sleepiness. An old adage warns that you cannot burn the candle at both ends. Yet many people still insist on trying.
- Circadian rhythm sleep disorders: These are disorders of irregular rhythm caused by factors like shift working, where the person has to work during the normal sleep period.
- Narcolepsy: Here a person has a tendency for excessive sleepiness and feels refreshed after short naps. In addition, he has other features of narcolepsy, like cataplexy and sleep paralysis.
- Other sleep disorders: like Sleep Apnea, Restless Legs Syndrome and Periodic Limb Movement Disorders can cause excessive sleepiness due to repeated disruption of nighttime sleep.
- Psychiatric disorders: Major depression can cause excessive sleepiness.
- Substance abuse: Abuse of sleeping pills, sedatives, and alcohol can cause excessive sleepiness.
- Medical conditions: Conditions such as brain tumor, morbid obesity and chronic pain may cause excessive sleepiness.
The above-mentioned conditions may lead to Excessive Daytime Sleepiness.
When excessive sleepiness cannot be explained by any of the above-mentioned disorders, then, it falls into a category of disorders termed hypersomnia.