Google 'sleep paralysis' you will find that many have had the same experience with many similarities. It is possible that sleep paralysis is related to an unexplained dip in potassium levels during the experience, but relatively normal levels otherwise. Of course, those are serum levels which are not a good indicator of potassium levels in the body as it is stored in the cells not the serum.
Anyway, several individuals' experiences are marked with both loud sounds and out of body experiences. I personally believe that the out of body part is more real even if many of the other events seem like a perpetuation of the dream one was having when they awoke. The brain chemistry is powerful stuff.
The article below touches on various types of periodic paralysis states, and some individual experiences.