Maybe it is because I've been participating in this thread, but I finally had the "old hag" experience last night. Except for me it wasn't an old hag, but a very generic "someone" in the room who didn't belong there - running back and forth from one side of the bed to the other. It reminded me very much of when we had a break-in in 1998 and the guy got into our bedroom while we were sleeping. It was terrifying - I couldn't get back to sleep after that and finally turned the light on and read for quite a while. When my partner finally came to bed he found me sleeping with the light on and my book by my side.