At the moment of orgasm there can be a sudden, severe pain in the neck and head. This is probably due to contraction of some of the small blood vessels in the brain, similar to migraine, and in fact half the people with this type of headache are also migraine sufferers. This pain generally lasts less than an hour, but may be gone in 10 minutes or linger for a few hours. It may be throbbing, dull or stabbing. Less commonly, as sexual excitement increases, some people experience a dull, cramping, tight feeling at the back of the head. This is probably due to excessive contraction of the muscles of the neck. Some people have only one of these headaches, but many people have a combination, so they experience a headache that increases with sexual excitement, and culminates in an explosive headache at orgasm. Other causes of headache during sex are pills for the treatment of erection problems, such as Viagra (sildenafil), headache is one of their side effects. We recommend you to see a General physician to evaluate its cause. During the acute episodes you can relieve it Ibuprofen 200 mg and hot shower.

I had the exact symptoms as you and I thought I had some awful ailment. A visit to the doctor revealed that I had simply strained my neck. During my doctor's visit, the Doc looks at me and asks, "did you just buy a motorcycle?" and I replied, "yes". Well, it turns out that the new helmet added some weight that my neck was not used to and , during sex (ejaculation), would result in those painful spasms that would shoot through my neck into the back of my head. A week of no riding was all the medicine i needed and I've never had that happen again. Maybe you strained your neck as well. Hope that helps

I had the very same symptoms. Turns out I strained my neck from wearing a helmet after buying a motorcycle. A rested my neck for a week and all was well.