Oh my gosh, this is sooooo weird! I seriously thought that I was the ONLY woman that had ever experienced this because whenever I've said something to ANYONE, they'd look at me like I was crazy or something!
But there's a slight difference between mine and yours. In my dreams, I don't actually HAVE an orgasm - I get right to the point where it feels good then out of nowhere, I wake up with these terrible pains like period cramps. Is this what yours feel like? I've noticed something though - which makes it even stranger....every time I have these pains, I always end up having to go #2 or I have really bad gas. I wouldn't worry, I ran it past my OB because it worried me too and she told me that it was normal to feel things you've never felt before and that cramps (as long as they aren't constant and severe) are normal.
I am 10w3d today, and I still can't even think about sex - it repulses me to the point where my husband tried to arouse me one night and I had to stop him because it literally made me gag.
I'm sorry I couldn't answer your question more in depth, but I do want you to know that you are not alone. Good luck and keep us posted.
In the book What to Expect When you're Expecting [i'm pretty sure that's the right one] and in others, it states that this is actually nothing to be alarmed about. It pretty much just said that it's normal... sorry that's all the help i can give you. i don't know why it happens. :S