“Hypersomnia” means sleeping too much, especially irresistible sleep episodes during the day.
The most common cause of hypersomnia is a breathing disorder, such as obstructive sleep apnoea. This is extremely common. If you snore, you have a very high chance of having this condition. If, in addition to snoring, you are falling asleep at times you do not want to, then this is most likely obstructive sleep apnoea, although other conditions can do the same thing. Obstructive sleep apnoea can have a number of important medical consequences, and needs medical attention.
Another common cause of hypersomnia is Restless Legs. This is typically a feeling of restlessness in the legs when one gets into bed at night. During sleep there are small movements, which may go unnoticed by the sufferer or their bed partner, which can cause arousals. The arousals may, themselves, also not be noticed. This can also cause severe daytime sleepiness. The treatment is usually with a small dose of the appropriate medication used every night.
An uncommon cause is narcolepsy. Although many people have heard of this condition, it is actually quite rare. Because treatment is generally lifelong, with quite powerful medication, it is important to have this properly diagnosed by a sleep professional.