Insomnia is a symptom of a sleeping disorder characterized by persistent difficulty falling asleep or staying asleep despite the opportunity. Insomnia is a symptom, not a stand-alone diagnosis or a disease. By definition, insomnia is "difficulty initiating or maintaining sleep, or both" and it may be due to inadequate quality or quantity of sleep. It is typically followed by functional impairment while awake. Both organic and non-organic insomnia constitute a sleep disorder.
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