[perhilzit]

I had several experiences in "sleep paralysis" (the first stage at the beginning of an OBE) where as long as I was immobile, there would be complete silence, but as soon as I tried to get up, I would hear like a crowd of 100 children screaming "AAAAAAHHHHH!!!!!" very loud behind me, with strong vibrations all over my body. As soon as I stopped trying to move, it would go calm again. I think the reason it happened was because I was trying to use my physical muscles to get up, instead of my "astral muscles" -- in order to get out, I had to "feel for" my astral body and transfer out of the physical first, using a visualization technique. I had a very similar experience...I woke up and felt like the left side of my body had separated and the rest had not. I tried to sit up but found myself paralyzed. Just as I tried to sit up I heard a horrible high pitched scream from my left. It was intense, and was followed by more terrifying paralysis. I think your explanation makes sense, it is exactly what I thought happened to me.