1st. Cluster head ache. Like a migraine but 10x worse. You honestly would blow your brains out if you had a gun to hand and were in any condition to manage one. It's like having a rusty javelin going in through your right eyeball and all the way through that side off your brain. I wouldn't wish it on anyone.
2nd. When I broke my collar bone while wearing a wetsuit. The tightness of the wet suit constantly pulled the broken bone out of place. It was fucking agony. It was a brand new expensive wet suit but at the hospital I was begging them to cut it off.
I've broken loads of bones. Broke my arms 5+ times, nose 3 times, elbow, toes, fingers etc - nothing hurt more than the collar bone, because of the wet suit.
3rd. Having a dislocated elbow relocated. My arm had telescoped up, so whats normally my elbow was sticking out where ones tricep usually is. They had two ambulance chaps holding my shoulders back while a doctor had his knee against my chest while pulling my arm out to its more usual length.
That smarted a bit, I can tell you.
More painful than childbirth, according some women cluster headache sufferers!