Hypersomnia

Hypersomnia is a medical condition which is characterized by unusual sleepiness. People with hypersomnia easily feel sleepy during the day, and fall asleep. The condition where people wake up often during the night, and have trouble sleeping through the night is called insomnia and is different. Hypersomnia is a sleep disorder. 
Hypersomnia affects about five percent of the population, or about one of twenty people. Very often, people with Sleep apnea suffer from hypersomnia. Hypersomia can also occur with other conditions, such as mood disorders. 
If the hypersomnia is caused by a problem with the brain or nervous system, it is called primary hypersomnia. Narcolepsy is an example of a primary hypersomnia. If the hypersomnia is the effect of another condition, it is usually called secondary hypersomnia. Examples of secondary hypersomnias include someone losing consciousness because of epilepsy. Sleep apnea, cited above, is one of the most common forms of secondary hypersomnia. Certain drugs can also cause (secondary) hypersomnias.
Primary hypersomnias are very rare. Secondary hypersomnias are quite common.