WASO-Specific Autonomic Instability in Paradoxical Insomnia: A Stage-Resolved HRV Analysis

Paradoxical insomnia is characterized by a discrepancy between subjective sleep com-plaints and objectively preserved sleep, yet its autonomic mechanisms remain poorly un-derstood. This study examined stage-specific autonomic characteristics of paradoxical insomnia using heart rate variability (HRV)–based statistical, multivariate, and machine learning analyses in a large population-based cohort. HRV features were extracted from non-overlapping five-minute windows across non–rapid eye movement (NREM) sleep, rapid eye movement (REM) sleep, and wake after sleep onset (WASO), and compared among paradoxical insomnia, objective insomnia, and normal sleep groups. Whole-night and consolidated sleep–stage HRV features showed substantial overlap among groups. In contrast, consistent stage-dependent differences emerged selectively during WASO, dur-ing which paradoxical insomnia exhibited distinct autonomic patterns relative to both comparison groups. Multivariate analysis showed the greatest group displacement dur-ing WASO, with UMAP centroid distances exceeding those observed during NREM and REM sleep. Supervised models trained on WASO-specific features achieved the highest classification performance, yielding an accuracy of 0.61 and an F1-score of 0.69 for para-doxical insomnia versus normal sleep, although overall discriminability remained mod-est. These findings indicate that autonomic alterations in paradoxical insomnia are pref-erentially expressed during post–sleep-onset wakefulness. Stage-resolved analysis identi-fies WASO as a physiologically informative window for objective phenotyping and for characterizing heterogeneity in insomnia subtypes.