I thought the same thing. I was just recenty diagnosed with a thyroid condition and started new medications to help treat it. A few weeks into my new meds i had the same thing happen. I woke up having an orgasm. I told my wife about it and she thought it was rather strange. I felt strange myself but i guess it is normal. I find it strange typing in this topic on the web. LOL..
It's nothing to worry about. Its uncommon but a lot of women experience this, especially during pregnancy. If I were a better advisor I'd rememebr the name for this but it's slipped my mind. Basically you're having an erotic responce in your sleep. It's believed to be caused by lurid dreams but there's no real way to test that.