But up until now there's been few hints as to the cause of cluster headaches. Australian Dr Peter Goadsby is Professor of Clinical Neurology at University College, London, and he heads up the Headache Group at London's Institute of Neurology, leaders of research in the area.
Cluster headache is probably the worst pain that humans experience.
I know that's quite a strong remark to make, but if you ask a cluster headache patient if they've had a worse experience, they'll universally say they haven't. It's like somebody's pushing a finger or a pencil into your eyeball, and not stopping, and they just keep pushing and pushing, because the pain's centred in the eyeball, and nothing else has ever been that painful in my life. So you can imagine that these people give birth without anaesthetic once or twice a day, for six, eight or ten weeks at a time, and then have a break. It's just awful. You suddenly realise that you have a pain behind your eye.