Night-to-Night Sleep Variability Modulates Subjective Sleep Perception in Chronic Insomnia: A Multilevel Analysis.

Introduction: Subjective sleep perception often differs from objective sleep measures in chronic insomnia, but the role of night-to-night sleep variability remains insufficiently understood. This study examined the effects of daily within-individual sleep fluctuations and between-individual sleep variability on subjective sleep perception in patients with chronic insomnia. Methods: Fifty patients with chronic insomnia completed home-based sleep monitoring and sleep diaries for five to seven consecutive nights, yielding 312 valid nights. Sleep perception bias was defined as the difference between objective sleep parameters and subjective estimates. Sleep variability was quantified using the coefficient of variation. Linear mixed-effects models examined within-individual associations, between-individual variability effects, and cross-level interactions. Results: Nightly objective changes in total sleep time, sleep efficiency, wake after sleep onset, and sleep onset latency were significantly associated with corresponding subjective-objective discrepancies. Subjective perception changed less than objective sleep parameters, suggesting reduced subjective responsiveness to nightly sleep changes. Between individuals, lower total sleep time variability was associated with greater bias in perceived sleep duration and sleep efficiency. Higher N2 percentage variability was associated with greater wake after sleep onset perception bias and moderated the association between objective wake time and subjective perception. Discussion: These findings suggest that subjective sleep perception in chronic insomnia is influenced by nightly objective sleep changes and longer-term sleep variability. N2-related findings should be interpreted cautiously given the exploratory sleep-stage-specific analyses and portable EEG monitoring.