Sleep and primary headaches.

The relationship between sleep and primary headaches has been known for over a century, particularly for headaches occurring during the night or early morning. Migraine, tension-tyre headache, and cluster headache may cause sleep fragmentation, insomnia, and hypersomnia, causing considerable social and economical costs and several familial problems. By contrast, sleep disorders may themselves trigger headache attacks. Finally, headaches and sleep disorders can also be symptoms of other underlying pathologies. Despite this background, there is still no clarity about the mechanism that links these two entities and their interdependence remains to be defined. Patients with primary headache should undergo a careful assessment of sleep habits.