Insomnia is highly prevalent in patients with long-term medical conditions. Although fatigue is the most common daytime symptom of insomnia, it is still largely unknown which underlying components...Show moreInsomnia is highly prevalent in patients with long-term medical conditions. Although fatigue is the most common daytime symptom of insomnia, it is still largely unknown which underlying components are associated with fatigue in a broader population of insomnia patients. Previous literature stated that dysfunctional sleep-related beliefs (DSRB) and pre-sleep arousal (PSA) could explain the relationship between insomnia and fatigue. Additionally, subjective sleep characteristics, such as insomnia severity, number of nocturnal awakenings (NoA) and sleep efficiency might also be components of this relationship. This study aimed to investigate how these factors affect fatigue in a broad medical population with insomnia. It was hypothesized that more disturbed sleep-related psychological factors and subjective sleep characteristics were associated with increased fatigue. This cross-sectional study, derived from the ongoing TIMELAPSE study, consisted of 154 participants. Participants completed questionnaires assessing fatigue (Checklist Individual Strength-20), DSRB (Dysfunctional Beliefs and Attitudes about Sleep-16), PSA (Pre-Sleep Arousal Scale), and insomnia severity (Insomnia Severity Index). The Consensus Sleep Diary tracked NoA and sleep efficiency daily for one week. Two multiple regression analyses were performed to assess the relationship between sleep-related psychological factors (DSRB, PSA), subjective sleep characteristics (insomnia severity, NoA, sleep efficiency) and fatigue. Age, gender, and depression were included as controlling variables. Results showed that DSRB (β = .174, p = .027), PSA (β = -.160, p = .036), and insomnia severity (β = .243, p = .002) were factors associated with fatigue in insomnia patients. More severe DSRB and higher insomnia severity predicted elevated levels of fatigue. Contrary to expectations, PSA was negatively associated with fatigue. Lastly, NoA and sleep efficiency were not related to fatigue. This study uncovered connections between more severe DSRB, lower PSA, and higher insomnia severity that led to higher levels of fatigue. The current study suggests that improvements in DSRB and reducing insomnia severity may reduce fatigue of insomnia patients with long-term medical conditions. Sleep interventions should emphasize on challenging these DSRB. Future research is needed to examine the complex relationship between PSA and fatigue, as well as whether changes in DSRB during CBT-I treatment reduce fatigue symptoms in this population.Show less