I know a woman who has recently begun to experience a debilitating, near-migraine headache immediately prior to orgasm. Needless to say, she is pretty freaked out by this.
Anyone know what causes this or, more importantly, how to make it stop?
Odd.
My wife usually gets headaches to prevent orgasms. Or at least my attempts to give her one. 
Would it have anything to do with blood flow and/or blood pressure?
I (a guy, FWIW) used to get a headache immediately after having a really intense orgasm. My guess was that it was caused by a rapid change in blood pressure.
IANAD, and that’s why I’m saying – she should see a neurologist, pronto. This could be a benign condition that can be fixed by taking a migraine medication at the right time, or it could be very dangerous. Ain’t no way a bunch of folks on a meesage board who haven’t seen her can tell.