I've heard about this a LOT on these boards. It is more common than most people think. I've never experienced it and I'm jealous BUT everyone has always said that it doesn't harm anything. You can't avoid what you have no control over and you shouldn't freak out about it either. If you feel more comfortable you can call your RE but honestly I don't think you have anything to worry about.
So, you've heard of this before! Thank God. I thought I was the only one. My RE had me on Valium for 24 hours to keep my uterus still and not contracting and then this! Ugh.. Thank you so much for your answer. I'd call the RE, but what are they gonna tell me? Don't do it again?! I feel like a dork.