Cluster headaches are a group or cluster of frequent headaches. The cluster may last for weeks or months, usually followed by long periods of no headaches. This remission period can last for months or years.

Pain from cluster headaches is usually severe on one side of the head, and is accompanied by other symptoms like nasal discharge and red, teary eyes. The patient may also feel restless and agitated.

Cluster headaches are often said to be the most painful kind of headache. Injected medications, preventive medications, steroids, and inhaled oxygen are treatments that may help.