One of the most frequent cause of hypersomnia is narcolepsy. Victims of this strange disorder do not necessarily feel tired during the day; however, they are frequently overwhelmed by sudden, uncontrollable attacks of sleepiness. One of the most prominent—and troubling—features of narcolepsy is cataplexy, or muscle paralysis, a symptom that distinguishes this condition from other forms of hypersomnia. Narcolepsy accounts for roughly one-fourth of all DOES diagnoses. In fact, seven out of ten patients who are seen by sleep laboratories are diagnosed as having either sleep apnea or narcolepsy.

Less frequently, DOES may be the result of nocturnal myoclonus if the leg jerks are powerful enough to cause partial arousal during sleep. Like apneics, victims of myoclonus may be unaware their sleep has been disrupted, noticing only that they are still tired the following the day. Other sources of daytime sleepiness include psychiatric disorders such as depression, use and abuse of drugs or alcohol, and a whole range of metabolic, endocrine, and central nervous system disorders. When we are unable to identify a specific cause for hypersomnia, we classify it as “idiopathic,” which means “caused by itself” or “of unknown origin.” Nearly one out of ten cases of DOES fits this vague but convenient category. I will also devote part of this chapter to a discussion of another variety of sleep problem, disorders of the sleep-wake schedule (DSWS) which, though of a different nature from DOES, can also produce the symptom of daytime sleepiness.

As we will see, diagnosis of DOES can be tricky. Daytime tiredness can mask a number of other problems, including drug use, poor nutrition, emotion frustration, dissatisfaction, or poor motivation. Many forms of psychological disruption can sap our energy, disturb our rest, and exhaust us even more than strenuous physical activity. Lifestyle can contribute as well: if you lead a sedentary life, for example, you omit the exercise that gives the body the chance to purge itself of waste products and restore energy to the muscles.

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