Heh, you guys have had things sit on you at night, although I'm sure these experiences are damn freaky, it sounds a little funny when you describe things sitting on you.
I myself have not had this experience. The only night-attack/nightmareish incident I've ever experienced was waking up in the middle of the night, at age 4 or 5, to my whole bed (frame and all) shaking rather violently. It stopped the instant my dad busted in the room after hearing me scream like a little girl.
On the other hand, my sister experiences it quite often, now I'm interested, and will have to do some more reading on this....so I can freak her out even more