Cluster headaches are extraordinarily painful brief headaches which appear in groups, or clusters, in cycles which can last for weeks or years. It is believed that cluster headaches are among the most extreme pain which humans can experience, and the intense physical experience of cluster headaches has been known to drive patients to desperate measures. There is no cure for cluster headaches, although several medications can be used to treat patients during an attack, or to help prevent the headaches. In extreme cases, surgery may be offered.

Like many other chronic headaches, the trigger for cluster headaches is unknown. They often appear suddenly, without any type of warning, and can disappear within minutes or hours. It has been suggested that cluster headaches may be linked to specific foods, such as alcohol, caffeine, and chocolate, and a doctor may place a patient on an elimination diet as part of a treatment plan. They may also be related to the natural cycles of the body, since cluster headaches often appear on a regular and predictable basis.

The mechanism of cluster headaches is understood. They are a type of vascular headache, meaning that the symptoms are caused by the dilation of blood vessels. The blood vessels put pressure on the trigeminal nerve, causing intense and sharp pain. Patients have described the headaches as resembling hot pokers being forced into the eye or skull. Generally, cluster headaches attack only one side of the face, and are accompanied by symptoms such as a runny nose or drooping eyelid.

A patient of any age can experience the onset of cluster headaches, although most patients are between 20 and 40. The headaches start with two to three attacks each day for a period of four to eight weeks, and then the cluster headaches usually stop for around a year. These episodic cluster headaches will continue to run in cycles of attack and remission. Chronic cluster headaches appear with no remission, and can be very debilitating. Sometimes, a period of remission can last for decades, and in some cases, cluster headaches disappear entirely eventually.

The pain of cluster headaches can interfere with sleep, mental health, and daily life. In rare instances, patients have been known to commit suicide or self harm in an attempt to deal with the pain. Doctors keep a close eye on their patients to prevent this from happening, and a patient who experiences unbearable cluster headaches may be offered surgery on the nerve to attempt to reduce the pain. Fortunately, cluster headaches are extremely rare, occurring in approximately 69 out of every 100,000 people.