Clinical classifications of insomnia and its host of conditions and causes are extensive and specific. The spectrum of causes suggests that it is difficult to obtain good sleep and that sleep is, in fact, a delicate environment, the path toward which may be strewn with obstacles.

Insomnia is not a disease; rather, it is a complex symptom that results from insufficient sleep or sleep of poor quality. However, insomnia is distinguishable from short sleep. Many people sleep less than 75% of conventional eight-hour sleep time and experience no difficulty sleeping or waking. Insomnia is divided generally into two main categories: sleep onset insomnia and sleep maintenance insomnia. Sleep onset insomnia is the inability to fall asleep naturally. Sleep maintenance insomnia is the inability to stay asleep or to resume sleep after waking in the middle of the sleep cycle. A person may experience both sleep onset insomnia and sleep maintenance insomnia, which leads to both insufficient and poor sleep.

Insomnia can be categorized further as acute or chronic. Acute insomnia is self-limiting, meaning it runs its course in a few weeks or months and ends without being treated. Chronic insomnia lasts longer than three months and often needs to be treated. Insomnia can be caused by medical problems, such as chronic pain syndromes; psychiatric problems, such as depression; or primary sleep problems, such as periodic limb movement disorder (PLMD).

INCIDENCE

The prevalence of insomnia is unknown. Surveys of the general population suggest that 49% of adults report having brief periods of difficulty sleeping. About 10% of adults claim they have had insomnia lasting two weeks or longer, and, usually, about one-half of those who claim to have periods of difficult sleep also claim it is a significant problem in their lives. Since insomnia is frequently a symptom of illness, severe stress, trauma, and so on, its incidence varies with regard to age, sex, and severity of the predisposing condition.