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.