Hypnic headache is one of several relatively uncommon headache syndromes that may occur either as a primary headache or as a headache secondary to potentially malignant processes. Careful evaluation for underlying causes is important for these uncommon types of headache.
This topic will review hypnic headache. Other types of uncommon primary headache disorders are discussed separately. (See "Primary stabbing headache" and "Primary cough headache" and "Exertional headache" and "Primary headache associated with sexual activity" and "Thunderclap headache" and "Nummular headache".)
Also known as "alarm clock" headache, hypnic headache is characterized by episodes of dull head pain that develop only during sleep and awaken the sufferer from sleep . It is one of the few headache disorders to occur almost exclusively in later life.
Hypnic headaches typically occur frequently (≥15 days per month), and persist for at least 15 minutes after awakening the patient. They generally last no more than three hours, although longer durations may occur. About two-thirds of hypnic headaches occur bilaterally. The headaches are usually of mild to moderate intensity but may be severe in about 20 percent of cases .
While current diagnostic criteria for hypnic headache require dull head pain , throbbing pain and/or migraine features are not uncommon in patients with hypnic headache. A study that reviewed 71 cases of hypnic headache found that pulsatile headache was present in 38 percent . In two of the largest series of patients with hypnic headaches, involving 22 subjects from France and 17 from Taiwan, approximately one-quarter of subjects reported a headache that was not dull [4,5]. In most of these patients, the headache was throbbing or pulsatile.