Oh my Farking God they hurt so much. It literally feels like a grenade going off at the base of my skull.
For reference, I've punched another human being in the face so hard that I shattered their face mask, their nose and my wrist in one fell swoop, laying them out on the ground before taking down a second football player and lightly strangling them (they had it coming, one of the bastards sucker punched me).
I then played with that broken wrist for another six months before seeing a doctor because "hey, my wrist has been hurting for half a year, maybe I should see someone"
I've had an entire football team pile up on me, mangling my leg so bad that when I got up my ankle had a literally Orange sized lump on it, and then walked off the field no problem.
I've been (hilariously) mauled by a wild boar.
I've been burned, cut, beaten, stabbed, bloodied, bruised, and beaten again, but nothing has ever hurt me as much as that damn headache did/has been doing.
It's what I get for not paying attention to all that crap about breathing properly during intense exercise. Turns out I have to stay away from high intensity excercise for about two months because of this now.