But if you're one of the unlucky few, you won't forget it.
Cluster headaches affect less than one per cent of the population.
Men are six times more likely than women to get them, often starting in their 20s. The pain is excruciating, a severe throbbing around the eye that can last a few minutes or a couple of hours. The discomfort is such that some patients are driven to the point of suicide. There are still many unanswered questions about the exact mechanics of a cluster headache and how it affects blow flow around the brain. A class of pain relievers known as triptens seem to help, as does breathing oxygen.