The shopping list of symptoms arrive one by one, the drooping eyelid (ptosis), the redness of the covering of the eyeball (conjunctival injection), the runny nose (rhinorrhea), the abnormal tearing (lacrimation). Pacing is the only way to deal with it or rocking in a foetal curl, grabbing knees and shins and squeezing hard as the cluster reaches in through your eye socket, makes you pummel your own head with a fist clenched in agony not anger.

Imagine this can happen at any time, can wake you when you sleep, sweep you up in its metronomic pulses, punishing at the same time every day or every week, making you a slave to your circadian rhythm. The cluster in your head, linking days and weeks into pods of suffering, takes your breath, steals your sight and removes the world, leaving just the burning hand that squeezes your brain and only lets go to squeeze all the harder next time around.

The names it hides behind are many. Erythroprosopalgia of Bing. Ciliary neuralgia. Erythromelagia of the head. Horton’s headache. Histaminic cephalalgia. Petrosal neuralgia. Sphenopalatine neuralgia. Vidian neuralgia. Sluder’s neuralgia. Hemicrania angioparalyticia. Vascular headaches that dilate blood vessels, squeezing the trigeminal nerve. V, the fifth nerve, responsible for sensation in the face.

It feels as though my brain wants to kill me. Has tools and knives and torture devices it employs. Some experts believe it to be the most severe pain known to medical science. Imagine that root canal infection you had a few years back. Imagine the vice squeeze of pain that wound slowly in your jaw. Imagine that happening again. Only the pain killers from the dental hospital can’t touch it. Nothing can. Then turn the agony you felt up to eleven and you might have some idea.

Ask cluster patients if they have felt worse pain and all will agree they haven’t. Women sufferers will tell you it is worse than giving birth. Imagine that. Imagine giving birth every day, regular as clockwork, for days on end. How about months. Try years. Imagine jabbing a red hot poker in your eye at regular intervals. For months. For years.

Get your head fitted with a spike, a fat iron spike, get someone to hammer it in through the very top of your skull, a spike long enough to radiate agony down into your neck while the thick hammered end protrudes from your skull. Imagine having a limb amputated without anaesthetic. Imagine an ocean of pressure crushing your skull, drowning you under atmospheres of pain. Imagine removing your brain and repeatedly running over it in your car. Imagine doing these things every day. Every week. For months. For years.

Then imagine yourself understanding why I have done this. Imagine how much I didn’t want you to have to find me, here in the car, a hose running from exhaust to window. Imagine yourself forgiving me. Imagine how sorry I am. Imagine how hard this was.

Illustration: The Cluster Headache by J.D. Fletcher