There are many variations of sleep disorder. The most common are hypersomnia, sleep apnea, insomnia and narcolepsy.

Hypersomnia is characterized as extreme sleepiness during the day, even with adequate sleep the night before, or prolonged sleeping at night.

Sleep Apnea is a breathing disorder where you wake because your breathing has been interrupted briefly throughout the sleep cycle.

Insomnia is an ongoing difficulty in falling asleep, staying asleep, or an interval of restless sleep.

Narcolepsy is caused when the brain is unable to properly regulate awake and sleep cycle processes resulting in symptoms that may include excessive daytime sleeping or untimely urges to sleep or vivid hallucinations while going to sleep or awakening. ( link to http://www.webmd.com/sleep-disorders/guide/narcolepsy )