Aetiology

The causes of excessive daytime sleepiness may be divided into:

• insufficient quantity of sleep
  • probably the most common cause of EDS
    • a common extrinsic cause of insufficient sleep is lack of time because of work or social pressures
      • however, most people make up for insufficient sleep during weekends or holidays
      • insomnia, owing to an intrinsic hyperarousal state that affects sleep onset and maintenance, is the commonest cause of insufficient sleep
• poor quality of sleep
  • poor sleep (quality) can be classified as caused by extrinsic or intrinsic factors
    • sleep disturbance caused by extrinsic environmental noise, light, or medical disorders causing pain and discomfort is usually obvious
    • intrinsic sleep disorders—obstructive sleep apnoea and periodic limb movement syndrome—are common causes of disturbed sleep
      • these patients typically report sleeping for enough duration (eight hours or more) but their sleep is disturbed by recurrent arousals from obstructed breathing and leg kicking, respectively
        
• unwanted drug effects
• primary neurological disorders
  • narcolepsy, idiopathic hypersomnia, and circadian rhythm disorders are the main intrinsic neurological disorders affecting the sleep wakefulness centre in the hypothalamus

Reference:

• Drug and Therapeutics Bulletin (2004); 42(7):52-6.
• Brown J, Makker KM. An approach to excessive daytime sleepiness in adults. BMJ 2020;368:m1047