Hypnic Headache

Headache disorders are among the leading causes of morbidity and years lived with disability worldwide. Headaches have been classified into various categories based on the International Classification of Headache Disorders Criteria. Hypnic headache (HH) is a rare, primary headache disorder that occurs exclusively during sleep, usually simultaneously each night. Previously, HH was referred to as "the clockwise headache" or "alarm clock headache." The , classifies hypnic headache as a primary headache disorder. HH is characterized by attacks of dull headache that typically present after age 50, occur at least 10 times per month, and occur during sleep without associated autonomic symptoms. The attacks awaken the patient from sleep and usually last 15 minutes to 4 hours after waking. Hypnic headache is a chronic disorder that can last for many years, but has moderate remission rates with treatment. Patients with migraine and hypertension are more likely to develop HH. Nearly all patients with HH exhibit motor activity during the attack, such as getting out of bed, eating, drinking, showering, or reading when awakened by the headache. However, the restlessness is less severe than cluster headache and trigeminal autonomic cephalalgias. Other causes of nocturnal headache and secondary headaches should be excluded before confirming a diagnosis of HH.