that doesn't mean you can't answer her...
I'm almost 33wks pregnant, and I still find myself waking up on my back when I go to pee. like jillian said, she went the entire pregnancy on her back and her baby is just fine. But if you are really paranoid about it, get a body pillow (or just lots of pillows) and prop them against your back while on your side (preferably your left). That's what I do, and it usually helps for awhile.
As for the heartbeat in your ear, you are gaining blood volume. I had it as well, especially when I was cleaning and my heart rate went up. Sounds completely normal to me.
As for the orgasm thing, I'll switch you if you don't want it! If your dreams are very vivid, your body can take affect to them, and that's what it sounds like. Most women get 'sex dreams' while pregnant (I know I do) so it would make sense that your body is just reacting to them. Again, if you are scared about it or it seems too strange, you always have your doctor.
I wish you a happy healthy 6 more months! (remember pregnancy is 10 months! 40 divided by 4 isn't 9!)