Abbreviations: AHI apnea-hypopnea index, BMI body mass index, CH cluster headache, CPAP continuous positive airway pressure, ICHD International Classification of Headache Disorders, ICSD International Classification of Sleep Disorders, EHS exploding head syndrome, HH hypnic headache, MOH medication overuse headache, MRI magnetic resonance imaging, TMD temporomandibular disorder, OSAS obstructive sleep apnea syndrome, PH paroxysmal hemicrania, REM rapid eye movement, RLS restless legs syndrome, SRBD sleep-related breathing disorders, SB sleep-related bruxism, TTH tension-type headache.