Millions of people complain of sleep problems, from insomnia to excessive daytime sleepiness, to chronic fatigue and the irritability associated with unsatisfactory sleep. Sleep problems are an important aspect of several psychiatric disorders, notably mood and anxiety disorders. Sleep deprivation has also been identified as a factor in numerous other medical conditions, including diabetes and impaired immune function. No matter what its specific medical source, sleep deprivation possesses high societal costs-impaired driving, work-related accidents and chronically poor work performance. In...