Hypnic headache.

Hypnic headache (HH), originally described by Raskin in 1988 as a late-onset, "curious sleep-related headache syndrome," has also been called "alarm-clock headache" as it regularly awakens subjects from sleep at a set time of night. In general, onset of HH is late in life with a chronic course. The most important characteristics of HH are: occurrence exclusively during sleep, chronic pattern of attacks (>/=15 per month), short duration, dull pain, and absence of autonomic signs and symptoms. The criteria adopted by the Second Edition of the International Classification of Headache Disorders (ICHD-II, Headache Classification Subcommittee of the International Headache Society, 2004) do not take into account the location, duration, and intensity of the pain. This is probably because the pain features and patterns are quite variable. In most cases HH is a primary headache form, but, because it begins late in life, it is mandatory to exclude an underlying disorder. In particular, nocturnal headaches secondary to increased intracranial pressure, arterial hypertension, sleep apnea, or pain-killing medication overuse must be ruled out. The co-occurrence of other types of primary headache in the same period or in different periods of life has been reported in about 40% of HH patients.