Generally, people think that they need to sleep for at least 6-8 h a day. However, patients with dysfunctional beliefs about their sleep problem often go to bed early in the evening to obtain quick sleep [4]. They believe that an early bedtime may induce an early sleep onset. However, based on the two-process model, maintaining wakefulness for several hours is essential for falling asleep in a timely manner [5,6]. The two-process model of sleep regulation is one of the most prevalent conceptual models of sleep regulation, which posits that sleep is regulated by the interaction of a homeostatic process (Process S) with a circadian pacemaker (Process C). Especially, Process S sets forth that the sleep-inducing force increases as wakefulness is prolonged. Previously, we have reported that insomnia patients with sleep latency ≤30 min tended to go to bed late.7 We showed that the duration from the wake-up time to bedtime in patients with sleep latency ≤30 min (16.5±1.1 h) was longer than in the patients with sleep latency >30 min (15.8± 1.5 h, p<0.01). In addition, in the same paper, a short sleep latency was significantly correlated with a long duration from wake-up time to bedtime (r=-0.43, p<0.01). The study showed that a pressure to sleep (homeostatic drive) is also needed to promote good sleep, even though the circadian rhythm is adequate. Going to bed early might increase the time in bed (TIB) during the night. Therefore, we considered that the discrepancy between one’s desired total sleep time (TST) and desired TIB may be related to the severity of insomnia.

In this study, we defined a new sleep index, namely ‘discrepancy between desired time in bed and desired total sleep time (DBST) index.’ People who suffer from insomnia desire to sleep more and to fall asleep at an earlier time, and they often state, “I have no wish if I can have at least 6 hours of sleep!” In order to sleep for at least 6 hours, these individuals should go to bed 6 hours before their waking time (i.e., 11 pm bedtime and 5 am wake-up time). However, they tend to go to bed earlier in the evening to attempt falling asleep early, yet they wake up late in the morning since they cannot easily fall asleep. From this clinical observation in the specialized sleep clinic, we hypothesized that DBST may be associated with insomnia severity. A high DBST indicates that one desires to sleep more even though he/she states that they only require a short duration of sleep.

Preoccupation with sleep has long been established as a key factor for insomnia. Sleep preoccupation mediated the overall attributions for poor sleep and, specifically, sleep effort and sleep pattern problem attributions. According to Harvey’s model [2], excessively negative-toned cognitive activity, selective attention and monitoring, distorted perceptions, dysfunctional beliefs, and safety behaviors interact to fuel insomnia. These types of preoccupations with sleep begin at the point of waking and continue throughout the day. People with insomnia selectively attend to and monitor the physical sensations of the deficit throughout the day. Additionally, compensatory behaviors, such as taking a nap or drinking a lot of coffee, are used to solve the perceived deficit. Together, these appraisal processes and behaviors confirm the presence of a sleep deficit and create a vicious cycle of negative thinking and worry, leading to actual decrements in functioning. However, to the best of our knowledge, there is no previous literature on the mediating effect of preoccupation with sleep on the association between dysfunctional beliefs about sleep or DBST and insomnia severity.

In this study, we attempted to identify the factors that can influence the severity of insomnia of the general population, among depression, viral anxiety, sleep effort, or dysfunctional beliefs about sleep. Additionally, we examined whether sleep effort mediates the association between dysfunctional beliefs about sleep or the DBST index and insomnia severity. We hypothesized the following: 1) dysfunctional beliefs will be positively related to insomnia severity, 2) DBST will be positively associated with insomnia severity, and 3) persistent preoccupation with sleep will partially mediate the relationships.

This anonymous online survey was conducted during November 9-15, 2021; additionally, a total of 400 individuals of the general population voluntarily participated through the survey system of the professional survey company, EMBRAIN (www.embrain.com). The study protocol was approved by the Institutional Review Board (IRB) of the Asan Medical Center (2021-1490), and requirement for written informed consent was waived by the IRB. We collected information regarding the participants’ age, sex, area of residence, and marital status; however, we did not collect any identifiable personal information. In this survey, we also collected responses to questions on coronavirus disease (COVID-19), such as “Did you experience being quarantined due to infection with COVID-19?”, “Did you experience being infected with COVID-19?”, or “Did you get vaccinated?” to exclude the influence of the COVID- 19 pandemic on the results of this study. In addition, we checked the participants’ past psychiatric history with the question, “Have you had experience with or been treated for depression, anxiety, or insomnia?” and checked current psychiatric distress with the question, “Now, do you think you are depressed or anxious, or do you need help for your mood state?” This e-survey was developed according to the Checklist for Reporting Results of Internet e-Surveys (CHERRIES) guidelines; [8] additionally, investigators (S.C. and C.HK.P) tested the usability and technical functionality before its implementation. The sample size was estimated based on 30 participants per cell [9]. We allocated 30-40 samples for ten cells (two groups of biological sex×five groups of age), and 400 participants were enrolled in this study.

In general, depression is a significant factor influencing insomnia; [18] additionally, there is a bidirectional relationship between depression and insomnia [19]. Especially during the COVID- 19 pandemic, individuals have been shown to suffer from sleep disturbance or insomnia [20,21], and depression is one of the most significant predictors for the latter [22]. Post-pandemic insomnia was reported to be associated with higher levels of depression; [23] conversely, a change in sleep pattern due to COVID- 19 was significantly associated with depression [24]. Moreover, dysfunctional belief about sleep was a significant predictor of insomnia during the COVID-19 pandemic [25,26]. Dysfunctional sleep-related beliefs can be expected to be increased during the COVID-19 pandemic [26] and might affect the severity of insomnia.

However, in this study, anxiety regarding viral diseases was not a significant predictor of the insomnia severity of the general population during the COVID-19 pandemic. Previously, a high prevalence of anxiety and insomnia was reported among the general population [20,21]. Although we reported the possibility of the influence of anxiety on sleep disturbance among healthcare workers [27], the association of viral anxiety, assessed using the viral epidemic-specific rating scale, with insomnia was rarely reported among the general population. First, during the COVID-19 pandemic, we can presume that depression or stress, rather than anxiety, might be a strong predicting factor for sleep disturbances among the general population, although further studies are needed to provide evidence. Second, during the 2 years of the pandemic, individuals adapted to the viral anxiety, and it may be that their anxiety no longer influences the insomnia severity.

We observed that the DBST index was significantly correlated with insomnia severity from the correlation analysis, as we hypothesized. Furthermore, this might be the first study that showed that a discrepancy between one’s desired TIB and desired TST can predict the severity of insomnia. The concept of DBST originated from the idea that patients with dysfunctional beliefs about their sleep problem often go to bed early in the evening, since they believe that an early bedtime may induce early sleep onset [4]. However, they will not get up early in the morning, although they went to bed early in the evening. Therefore, going to bed early in the evening might increase the TIB during the night. Previously, we have reported that the duration from the wake-up time to bedtime in patients whose sleep latency was ≤30 min was longer than that of patients whose sleep latency was >30 min [7]. In addition, a longer duration from wake-up time to bedtime predicted a sleep latency ≤30 min in our previous study [28], which was conducted among cancer patients. This concept might affect the sleeping pill ingestion time.

In our previous study on the association between the sleeping pill ingestion time and satisfaction with sleeping pills [10], we reported that a shorter interval between pill administration and wake-up time increased patient subjective satisfaction with sleeping pills. Additionally, we proposed to advise patients to take sleeping pills approximately 7 h before their usual getting- out-of-bed time, not 30 min before bedtime, which can lead to confusion regarding the time the pills must be taken for patients to induce short sleep latency. Among cancer patients [29], we reported that reducing the duration from the sleeping pill ingestion to wake-up time can influence the satisfaction of sleeping pills. Furthermore, we proposed using the sleep in- dex time in bed during a day (TIB/d) as the total TIB during 24 h. This concept is also similar to the concept of DBST in terms of a homeostatic drive (Process S). In this study, we considered that a high DBST means that one presumes to sleep more even though they say they need just a short duration of sleep. We hypothesized that the insomnia severity will be correlated with a high DBST; additionally, we confirmed it from the results of this study.

Individuals with insomnia suffer unpleasant intrusive thoughts and excessive and uncontrollable worry during the pre-sleep period [30]. It is suggested that dysfunctional beliefs were a major source of worry and preoccupation. These erroneous beliefs about sleep are highlighted as exacerbating factors of insomnia and fuel the excessive negative cognitive activity and preoccupation [2]. Subsequently, counterproductive maladaptive coping strategies, such as excessive TIB and staying in bed while awake are adopted to cope with the excessive cognitive activity [31]. Cognitive processes, dysfunctional beliefs about sleep, distorted perception, and attention work to make individuals increasingly anxious and preoccupied with the sleep problem. These excessive worries and ruminations trigger the activation of the sympathetic nervous system, autonomic arousal, and emotional distress contributing to the maintenance of insomnia.

This study has a few limitations. First, it was conducted via an anonymous online survey system. This might lead to bias; however, we conducted this study via online surveys rather than face-to-face interviews, to prevent the risk of a viral outbreak. Second, the relatively small sample of participants selected from a national area might decrease the statistical power of this study. In the COVID-19 pandemic chaos, it is difficult to gather enough participants from all national areas via a face-to-face interview. Third, the concept of DBST is not still sound, and it might be biased since the responses came from participants via the anonymous online survey system.

In conclusion, we observed that depression, preoccupation with sleep, dysfunctional beliefs about sleep, and DBST influence insomnia severity in the general population. Additionally, we observed that a persistent preoccupation with sleep partially mediates the influence of dysfunctional beliefs about sleep and DBST on their insomnia severity. Though we do not know whether this relationship was shown since it was influenced by COVID-19 or whether it will be present in the normal situation in the absence of the COVID-19 pandemic, we consider that reducing the preoccupation with sleep might be effective in improving sleep problems. Further, the DBST concept can be a useful index for predicting the severity of insomnia.