Ok i was masturbating the other day and right when i was about to ejaculate I got an extremely sharp pain in the back right; almost upper neck part of my head(skull) and it's happened a couple more times since then whenever i maturbate and am about to ejaculate...It usually leads to painful throbs in my head(skull) or headaches....What is causing this...Is it nerves, my brain, my spine..Im really unsure and afraid it could be something seroius...THanks