Acute insomnia is characterized by the presence of difficulties in sleep initiation or maintenance that occurs at least three times per week for less than three months according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) (American Psychiatric Association, 2013). Acute insomnia is common and most people have experienced it, especially in response to situational stress or rapid changes in circadian rhythms. Notably, acute insomnia is at risk of evolving into chronic insomnia, which is defined by meeting DSM-5 criteria for insomnia disorder and symptoms lasting three months or longer (American Psychiatric Association, 2013).

Two prospective studies conducted by Ellis et al. reported that the annual incidence of acute insomnia is 36.6%, and 40% of those with acute insomnia develop chronic insomnia (Ellis et al., 2014, 2012). These findings suggest that acute insomnia is very common in the general population and a substantial proportion of people experiencing acute insomnia transit into chronic insomnia. It indicates that acute insomnia is a key transitional stage of chronic insomnia. Therefore, early intervention for acute insomnia may prevent chronicity. However, there are currently no guidelines for the treatment of acute insomnia, although cognitive behavioral therapy for insomnia (CBT-I) has been recommended as the first-line treatment for chronic insomnia (Qaseem et al., 2016).

In the past, short-term use of hypnotics was considered to relieve symptoms of acute insomnia (Sahoo, 2012; Chervin, 2014), whereas adverse effects are common, such as headache, nausea, tiredness, and drowsiness. Among non-pharmacological treatments, two trials conducted by Ellis et al. showed that brief versions of both individual CBT-I and group-based CBT-I effectively treat acute insomnia (Ellis et al., 2015; Boullin et al., 2016). These studies suggest that acute insomnia can be well managed by brief versions of CBT-I. Nonetheless, face-to-face CBT-I is limited in the real world due to high cost, the perceived inconvenience of traveling to face-to-face sessions, and a shortage of trained therapists as well as a large population with acute insomnia. Internet-delivered CBT-I can reduce such barriers but to date, it is still unclear whether internet-delivered CBT-I, a more accessible and low-cost one, is effective in treating acute insomnia, though many studies have proven excellent efficacy and feasibility of internet-delivered CBT-I for management of chronic insomnia (Cheng and Dizon, 2012; Espie et al., 2019; Ritterband et al., 2017).

Insomnia, especially when it becomes chronic, is associated with problems in the general population such as unhelpful sleep beliefs, daytime sleepiness, more pre-sleep arousal and sleep reactivity, and improper sleep hygiene, which may potentially maintain or exacerbate insomnia (Ellis et al., 2021). Previous studies show that CBT-I improves those problems among different populations (Chan et al., 2021; Redeker et al., 2022; Yang and Jun, 2022), and therefore we also aimed to assess the impact of the internet-delivered CBT-I on these problems among population with acute insomnia. Furthermore, evidence also shows insomnia is bidirectionally related to anxiety and depression and those emotional symptoms in the treatment of insomnia should also be concerned (Alvaro et al., 2013). Additionally, patients with insomnia tend to have impaired quality of life, which has become an important construct in contemporary medicine and health care (Kyle et al., 2010). Therefore, in this study, we aimed to 1) examine the effectiveness of a one-week internet-delivered CBT-I program to prevent the progression from acute to chronic insomnia; 2) investigate whether this one-week internet-delivered CBT-I program could improve insomnia symptoms, dysfunctional beliefs and attitudes about sleep, daytime sleepiness, pre-sleep arousal, sleep reactivity, sleep hygiene and practices, depressive and anxiety symptoms, and quality of life in patients with acute insomnia recruited from sleep clinics.