Sleep-wake disorders frequently give rise to severe ailments and varied distresses in a great number of people in the world, disturbing their physical and mental activities and their social function. Sleep-wake disorders are now classified into a great number of cate- gories according to their clinical features and etiological factors. Patients with sleep-wake disorders are taken care of not only by specialists for such disorders but also by general physicians and specialists of different physical and mental disorders. In the recent years, the nature of sleep and sleep-wake disorders have...