Has this happened?

This has happened to me twice now, and it's quite a bummer.

A couple months ago during sex I had this incredibly terrible pain in my lower abdomen/uterus area. I got chills, I felt nauseous, I couldn't move. It came on so suddenly. Nothing we tried helped (heat pack, water, stretching, food, sleeping) Eventually it subsided. Then it was just gone. And I hadn't felt anything like it until suddenly again today. Luckily it was no where as bad this time, and after a couple of hours I was back on my feet.

I have absolutely no clue what it is. Has anyone experienced this?