HeadacheRare nocturnal headachesCohen, Anna S; Kaube, HolgerAuthor Information Department of Clinical Neurology, Institute of Neurology, London, UK Correspondence to Holger Kaube, Department of Clinical Neurology, Institute of Neurology, Queen Square, London WC1N 3BG, UK E-mail: firstname.lastname@example.org Current Opinion in Neurology: June 2004 - Volume 17 - Issue 3 - p 295-299 Buy Abstract Purpose of review This review describes rare headaches that can occur at night or during sleep, with a focus on cluster headaches, paroxysmal hemicrania, short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing, hypnic headache and exploding head syndrome. Recent findings It is known that cluster headaches and hypnic headache are associated with rapid eye movement sleep, as illustrated by recent polysomnographic studies. Functional imaging studies have documented hypothalamic activation that is likely to be of relevance to circadian rhythms. These headache syndromes have been shown to respond to melatonin and lithium therapy, both of which have an indirect impact on the sleep-wake cycle. Summary There is growing evidence that cluster headache and hypnic headache are chronobiological disorders. © 2004 Lippincott Williams & Wilkins, Inc.