Functional neurological disorder and sleep disturbances: from comorbidity to mechanistic insight

Sleep disturbances are common in functional neurological disorder (FND), with meta-analytic evidence confirming their high frequency. Their relevance may extend beyond comorbidity, raising questions about their relationship to FND mechanisms and potential as therapeutic targets.

To synthesize evidence on prevalence, clinical profile, objective findings, and potential mechanisms of sleep disturbances in FND, focusing on subjective-objective discrepancies in sleep perception and vigilance-state assessment.

Structured narrative review of PubMed/MEDLINE from inception to April 2026. Evidence was appraised with Joanna Briggs Institute checklists and AMSTAR-2. Sleep disturbances were classified by ICSD-3-TR, with epidemiological, objective, and mechanistic findings summarized.

Discordance appeared in three domains: impaired self-reported sleep quality with less consistent actigraphic and PSG abnormalities; subjective sleepiness without MSLT sleep propensity; and events perceived during sleep arising predominantly from electroencephalographic wakefulness. In functional motor disorder, PSG showed longer REM latency, reduced sleep efficiency, and increased wake ratio, without correlation with self-reported measures.

Discordance recurs between subjective and objective measures of sleep, sleepiness, and vigilance state, although direction and magnitude vary across domains. We propose this pattern may be relevant to interoceptive and predictive-processing models of FND, although evidence remains limited and does not establish a disorder-specific mechanism.