Causes of excessive sleepiness include sleep apnea, circadian rhythm disorders and insufficient sleep.
Sleep apnea is a condition that causes the throat's air passage to close repeatedly during sleep, stopping breathing and disrupting the normal stages of sleep. The results of Sleep Apnea can be serious illness or even death caused by lack of oxygen. Symptoms include snoring, daytime sleepiness, gasping for air at night, irritability, personality changes, depression, chronic fatigue, insomnia and morning headaches.
Circadian Rhythm Disorders
Circadian rhythm disorders (CRD) is most commonly caused by shift work or multi-time zone air travel, CRDs are disruptions of the body's internal clock, which may cause sleepiness and/or insomnia at inappropriate times.
Narcolepsy is characterized by uncontrollable sleep attacks during the day, extreme sleepiness, falling asleep during an activity, losing muscle tone due to feelings of anger, surprise, amusement, or stress. This condition can be especially dangerous if the event occurs while the person is driving or operating heavy machinery. One cause, however, is a brain disorder called narcolepsy. Narcolepsy, caused by an abnormality in the brain's control of the sleeping and waking states, may cause muscle weakness, awakening with a sensation of paralysis, or dreaming while awake. This disorder is treated with a variety of medications.