What is insomnia

Insomnia (from Latin "in" meaning "not", and "Somnus" meaning "sleep") is most often defined by an individual's report of sleeping difficulties.^[1] While the term is sometimes used in sleep literature to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a positive response to either of two questions: "Do you experience difficulty sleeping?" or "Do you have difficulty falling or staying asleep?"^[1]
Thus, insomnia is most often thought of as both a sign ^[2] and a symptom^[1][3] that can accompany several sleep, medical, and psychiatric disorders, characterized by persistent difficulty falling asleep and/or staying asleep or sleep of poor quality. Insomnia is typically followed by functional impairment while awake. One definition of insomnia is difficulties initiating and/or maintaining sleep, or nonrestorative sleep, associated with impairments of daytime functioning or marked distress for more than 1 month."^[4]
Insomnia can be grouped into primary and secondary, or comorbid, insomnia.^[5][6][7] Primary insomnia is a sleep disorder not attributable to a medical, psychiatric, or environmental cause.^[8] A complete diagnosis will differentiate between:

• insomnia as secondary to another condition,
• primary insomnia co-morbid with one or more conditions, or
• free-standing primary insomnia.

From Wikipedia http://en.wikipedia.org/wiki/Insomnia