Insomnia disorder (ID) is a common condition that includes difficulty in initiating sleep, maintaining sleep, waking up too early, and nonrestorative or poor-quality sleep, all of which are commonly associated with symptoms of daytime functional impairment. According to a WHO collaborative study in 14 countries, 16% of correspondents had difficulty falling asleep; 25% of the correspondents either experienced difficulty staying asleep or woke up too early. The prevalence is even higher in the elderly and twice as high in women as in men.
Daytime complaints of people with insomnia concern cognitive functioning, fatigue, and depressed mood. Moreover, insomnia leads to higher risks of depression, anxiety and cardiovascular diseases. Daytime consequences and functional impairment caused a heavy economic burden to the society. It was estimated that the total annual cost of insomnia in 1994 was approximately $30-$35 billion in the USA. Now-a-days, the number should be much higher.