失眠是常見的臨床問題且成因複雜，對身心健康會造成許多不良影響且易合併憂鬱症等疾病，依定義及研究方法的不同，估計慢性失眠約占成年人口的10%-30%。目前失眠的診斷仍為臨床診斷，可以用PSG、MSLT、actigraphy 等實驗室檢查來輔助診斷。慢性失眠的產生涉及睡眠調節機轉，包括Process S(睡眠恆定)和Process C(日夜節律)，和維持覺醒及促進睡眠的神經系統。近一、二十年來的研究進一步了解到除了維持清醒的腦區和促進睡眠的腦區外，睡眠調節機轉還涉及食慾素/下視丘泌素 (orexin/hypocretin) 系統。在治療方面目前有藥物或非藥物治療方法可用來治療失眠，但合併藥物及非藥物治療的臨床效果更佳。

Insomnia is a common with complex etiological factors, and can have serious consequences, such as increased risk of depression etc. Prevalence of chronic insomnia is estimated as 10-30% in general adult population, depending on different definitions and methodologies. Diagnosis of insomnia is essentially a clinical diagnosis, and could be aided by laboratory examinations such as PSG, MSLT or actigraphy. Chronic insomnia could be understood in terms of dysfunction of sleep regulation mechanisms which include process S(sleep homeostasis) and process C(circadian rhythm), as well as nervous systems responsible for wake-promoting and sleep-promoting functions respectively. In addition, recent studies reveal the importance of orexin/hypocretin system. Management of insomnia consists of pharmacological and non-pharmacological therapies, and combined therapy is clinically a better recommendation than one of the above-mentioned therapies alone.