insomnia :

 Insomnia is a symptom, not a stand-alone diagnosis or a disease. By definition, insomnia is "difficulty initiating or maintaining sleepr both" or the perception of poor quality sleep. Insomnia may therefore be due to inadequate quality or quantity of sleep. Insomnia is not defined by a specific number of hours of sleep that one gets, since individuals vary widely in their sleep needs and practices. 

Although most of us know what insomnia is and how we feel and perform after one or more sleepless nights, few seek medical advice. Many people remain unaware of the behavioral and medical options available to treat insomnia.

Insomnia is generally classified based on the duration of the problem. Not everyone agrees on one definition, but generally: