I typed in the "crack" you were refering to, then went back and deleted it.
According to
<u>this</u> site, it's not uncommon and it's a "side effect" of the orgasm itself.
<u>This</u> site suggests it's caused by too much progesterone in the bloodstream (birth control pills...)
Then there's
<u>Here</u>:
Postdural headache: This is the least common of coital headaches. The pain occurs in the lower back of the head and is greatly increased then the patient stands. This form is more likely to be accompanied by nausea and vomiting.
Once diagnosis have confirmed coital headaches to be benign, medications can be taken one to two hours before anticipated sexual activity to hopefully avoid coital headaches. Some of the medications that may be used are Indomethacin, DHE (Dihydroergotamine, Imitrex, Zomig, Maxalt, Amerge, Midrin, Propanolol, and common analgesics. If the problem persists, daily preventive medications may be in order.