Cluster headaches are ‘the most painful condition on the planet’. Sufferers are going to extreme – and secretive – measures for relief

The condition is more excruciating than childbirth or gunshot wounds, but little understood. An online community of clusterheads' are self-experimenting with psilocybin - with promising results

Peter was working late, watching two roulette tables in play at a London casino, when he felt something stir behind his right eye. It was just a shadow of sensation, a horribly familiar tickle. But on that summer night in 2018, as chips hit the tables and gamblers' conversation swelled, panic set in. He knew he only had a few minutes.

Peter found his boss, muttered that he had to leave, now, and ran outside. By then, the tickle had escalated; it felt like a red-hot poker was being shoved through his right pupil. Tears flowed from that eye, which was nearly swollen shut, and mucus from his right nostril. Half-blinded, gripping at his face, he stumbled along the street, eventually escaping into a company car that whisked him home, where he blacked out.