About 5 years ago I have had sudden "major" headaches a few times. A few times after intercourse and once at my gym simply doing a "wall-sit". The gym headache was so severe it affected my eyes and I had to close them immediately. The throbbing was unbelievable and I had to sit down at the time. It lasted about 10 minutes and then it was gone without a trace. Like nothing even happened. I went to the Dr. and they sent me for a few MRIs but they couldn't detect anything. They told me it could have been a Thunderclap headache or high blood pressure (which I don't really have) - Anyway, I haven't experienced it since then until this month. I have had 2 of them again. Both at the gym. One doing squats with a weight on my shoulder and the other doing pull ups. I felt it coming on during the squat and stopped for a bit. The headache wasn't as severe and it went away.  Two weeks later during the pull-ups, I got to 6 and it hit me immediately. So severe that I couldn't speak and my head was throbbing worse than ever. Again, 10 minutes later, breathing through it, it went away without a trace. Like I couldn't even feel a trace of a headache.  My family is worried and its starting to worry me more.