Cluster headaches are rare, extremely painful and debilitating headaches that occur in groups or clusters.
Cluster headache sufferers typically experience severe headaches of a piercing quality near one eye or temple that last for fifteen minutes to three hours.
The headaches are usually unilateral and occasionally change sides.
Cluster headaches are classified as vascular headaches.
The intense pain is caused by the dilation of blood vessels which creates pressure on the trigeminal nerve.
While this process is the immediate cause of the pain, the etiology (underlying cause or causes) is not fully understood.
Cluster headaches often go undiagnosed for many years, being confused with migraine or other causes of headache.