Sleep disorders are defined as disorders which symptoms or pathophysiology are related with sleep regardless of comorbid physical and/or mental disorders. Sleep disorders are classified into 6 major categories: sleep related breathing disorders which exhibit abnormal breathing during sleep, sleep related movement disorders which show involuntary movements and/or abnormal sensations during sleep and/or nighttime, hypersomnia of central origin not due to other sleep disorders, circadian rhythm sleep disorders due to desynchronization between sleep-wake pattern and required social schedule, parasomnia which exhibit abnormal behavior during sleep and/or around sleep, and insomnia not due to other sleep disorders.