Cluster headaches are excruciating attacks of pain in one side of the head, often felt behind the eye.
Sufferers often call them 'suicidal headaches' because they're so severe.
Cluster headache attacks
Cluster headaches begin unexpectedly. They're much more painful than migraines or any other type of headache.
They're called cluster headaches because sufferers usually get one to three of these attacks every day, for several weeks or months, before they subside. A pain-free period will follow, which sometimes lasts months or years, before the headache attacks start again.
Each cluster headache lasts between 15 minutes and three hours (but often less than an hour). They may start in the early hours of the morning and wake the person from sleep.
Because of the intensity of the pain, some people will pace the room, rock, or bang their head against the wall out of frustration, restlessness and despair.
See Cluster headaches - symptoms for more information.
Types of cluster headache
There are two types of cluster headache, episodic or chronic (long-term).
About 10% of cluster headache cases are chronic.
Who is affected
Cluster headaches are rare and affect around 1 in 1,000 people. Anyone can be affected, but approximately 8 out of 10 people who have them are men and most are smokers.
It's not known what causes cluster headaches, but they're more common in autumn and spring. In some people, an attack can be triggered by drinking alcohol or an extreme increase in temperature (such as from exercising in hot weather). See Cluster headaches - causes for more information.
Treatment and support
Cluster headaches can severely affect quality of life, so it's important that sufferers are referred to a specialist clinic for treatments to relieve and prevent the attacks.
Although cluster headaches can cause great suffering, they're not life-threatening. They can often be relieved with a medication called sumatriptan or with oxygen therapy (see Cluster headaches - treatment for more information).
These treatments may vary in effectiveness from person to person. A few treatments may need to be tried before the attacks are under control.