What's the definition of insomnia?

Diagnosis: Insomnia is difficulty falling asleep, staying asleep, waking up before desired bedtime and being left tired during the day. This is definition from icsd-2.

See below: Insomnia is a sleep disorder in which one has the inability to fall asleep or to stay asleep as long as desired. While the term is sometimes used to describe a disorder demonstrated by polysomnographic evidence of disturbed sleep, insomnia is often defined as a pos response to either of 2 questions: "do you experience difficulty sleeping?" or "do you have difficulty falling or stay asleep".