Background: Hypnic Headache, also known as "alarm clock headache", is a rare primary headache disorder. It is characterized by frequently recurring headache attacks, which only develop during sleep, especially nighttime sleep.
Objective: This article gives a narrative review on the current knowledge about Hypnic Headache with a focus on secondary Hypnic Headache.
Methods: Based on literature research, using Pubmed and Google Scholar, latest case reports, studies, and systematic reviews about Hypnic Headache were analyzed and summarized focusing on therapeutic options and causes of secondary Hypnic Headache.
Conclusion: Hypnic Headache mainly occurs in elderly patients. However, younger patients and children may also suffer from Hypnic Headache. Many different causes of secondary Hypnic Headache are described in the literature and ought to be ruled out before diagnosing primary Hypnic Headache. The pathophysiology of primary Hypnic Headache remains unclear, but a dysfunction of the hypothalamus seems to play a key role.
Keywords: Hypnic Headache; ICHD-3; pathophysiology; secondary causes.