Stress and the hypothalamic–pituitary–adrenal axis: How can the COVID‐19 pandemic inform our understanding and treatment of acute insomnia?

Summary Stress and sleep are very closely linked, and stressful life events can trigger acute insomnia. The ongoing COVID‐19 pandemic is highly likely to represent one such stressful life event. Indeed, a wide range of cross‐sectional studies demonstrate that the pandemic is associated with poor sleep and sleep disturbances. Given the high economic and health burden of insomnia disorder, strategies that can prevent and treat acute insomnia, and also prevent the transition from acute insomnia to insomnia disorder, are necessary. This narrative review outlines why the COVID‐19 pandemic is a stressful life event, and why activation of the hypothalamic–pituitary–adrenal axis, as a biological marker of psychological stress, is likely to result in acute insomnia. Further, this review outlines how sleep disturbances might arise as a result of the COVID‐19 pandemic, and why simultaneous hypothalamic–pituitary–adrenal axis measurement can inform the pathogenesis of acute insomnia. In particular, we focus on the cortisol awakening response as a marker of hypothalamic–pituitary–adrenal axis function, as cortisol is the end‐product of the hypothalamic–pituitary–adrenal axis. From a research perspective, future opportunities include identifying individuals, or particular occupational or societal groups (e.g. frontline health staff), who are at high risk of developing acute insomnia, and intervening. From an acute insomnia treatment perspective, priorities include testing large‐scale online behavioural interventions; examining if reducing the impact of stress is effective and, finally, assessing whether “sleep vaccination” can maintain good sleep health by preventing the occurrence of acute insomnia, by preventing the transition from acute insomnia to insomnia disorder.