Introduction to Sleep Disorders

A total of 85 sleep disorders are described in the International Classification of Sleep Disorders, 2nd ed. Knowledge about those sleep disorders will be essential not only for good and healthy sleep but also for maintaining adequate physical and mental function during daytime. Sleep medicine has a relatively short history compared to other medical fields, thus, many sleep disorders are not familiar to the general public and even to physicians. In this small review about various sleep disorders, I will briefly introduce basic concepts about insomnia, sleep-related breathing disorder, hypersomnia, circadian rhythm sleep disorders, parasomnia and sleep-related movement disorders. These sleep disorders are frequently encountered in clinical settings, and understanding them will give us insight about the basic mechanism of sleep-wake states.