Disordered descent into sleep: microstructural divergence across arousal-linked conditions

Sleep onset is an unstable transition whose microstructure may distinguish clinical phenotypes. Using Hori 4-second microstaging in patients with narcolepsy type 1, idiopathic REM sleep behaviour disorder, NREM parasomnia and an exploratory fibromyalgia cohort, each with matched controls ( n = 48 pairs), we quantified timing, entropy, hemispheric laterality and sequence ordering. Narcolepsy showed compressed, irregular onset, fibromyalgia prolonged divergent onset, and the remaining groups near-normative trajectories, suggesting disorder-specific signatures of arousal instability.