From night-to-night and from person-to-person: dynamic phenomena of insomnia.

Study Objectives: Sleep is complex and variable, yet insomnia research and treatment often rely on averages-either across nights or across individuals. Such approaches risk obscuring dynamic features that characterize insomnia as a disorder and its unique manifestation in individuals. In this study, we explore disorder-specific (group-level) and person-specific (individual-level) dynamic phenomena of insomnia among people with insomnia. Methods: We analyzed 8 weeks of sleep diary data from 61 participants with insomnia. Four domains of sleep dynamics were examined at group- and individual-levels: (1) night-to-night variability, (2) temporal dependency of sleep quality, (3) stability of sleep complaints, (4) weekday-weekend variability. We correlated these domains with insomnia severity, pre-sleep arousal, and sleep-related safety behavior. Results: At the group-level, insomnia was characterized by (1) night-to-night fluctuations in sleep parameters, (2) unpredictable sleep quality, (3) frequent co-occurrence and fluctuations in type of sleep complaints, and (4) different sleep patterns on weekdays and weekends. These disorder-specific dynamic phenomena showed medium-sized significant correlations with insomnia indices, ranging from Conclusions: Sleep in insomnia varies from night-to-night and person-to-person. Reliance on averages across nights and across individuals may obscure fluctuations of potential clinical relevance. We call for broader use of sleep diaries to capture dynamic patterns of insomnia and for investigation of their clinical utility. Clinical Trial: Sleep Restriction Treatment for Insomnia.URL: https://clinicaltrials.gov/study/NCT05548907. Registration: NCT05548907.