Hypnic headache, or headache during sleep, is a rare primary headache disorder occurring only in the senior population, with onset typically around the age of 60. Women are more likely to experience hypnic headache than men. To be called "hypnic headache," the headache must occur exclusively at night or during the day during napping. The attacks are very painful, often awakening the afflicted individual at the same time each night. The patient may be awakened during a dream by diffuse pain and nausea.
Hypnic headache is throbbing in quality and occurs 2-4 hours into nighttime sleep, although attacks after daytime napping are reported. The duration is usually short-lived, lasting from 5 to 60 minutes. The throbbing and pain occurs on both sides of the head.
Hypnic headaches typically respond to lithium carbonate at a dose of 300 mg to 600 mg, although caffeine and indomethacin are also helpful. Because hypnic headaches affect only individuals over the age of 50, it has been suggested that there are disturbances to the "biological clock" related to serotonin levels in the brain. The absence of autonomic features that are often seen in migraine or cluster headache distinguishes this illness from these conditions.