Posted this on another thread but it might help.
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One similar episode I had was the often-reported-by-people being chased back to awakeness by a very nasty 'something' from a dream. People say they very nearly get caught and only JUST managed to wake up in time. Heart racing, etc when awake.
I had this dream a number of times until one day when I woke up scared, I realised that it was nothing to be scared about. What I was experiencing was my physical senses perceiving the return of my astral body and the scary monster I thought was persuing me was actually my astral body coming back to my physical.
After that I have had absolutely no more of these dreams. It was like I explained it to myself what was happening and now I am not scared (of that) any longer.
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Also, from what I read/understand everyone's astral body goes slightly out-of-phase with our physical body every night in order to get 'spiritually recharged' like a battery needing energy. This is why the 'falling' sensation often happens to folk, it is the quick re-intergration of the astral and physical bodies and is interpreted by your brain as a falling sensation.
People who can consciously astral travel or have OBE's do this in a conscious way and consciously separate and then decide to take their astral body further. However, if left alone and without consciousness (most people), the astral body will separate by only a small distance from our physical. Actually, it seems as if researcher Robert Monroe found that there are at least 2 other bodies which separate from the physical.
Sleep paralysis from an occult/paranormal point of view is a natural stage in the conscious separation process and is the withdrawal of bodily sensations from the physical body so that the consciousness can focus on the astral body. It is getting over this fear that allows the conscious astral travel which are what we now know as OBEs. Some people who cannot face the fear of this separation do it from their dream state. The separation process often causes cracks, pops, hums, bright lights, tinglings, etc different things for different people. By relaxing and going-with-the-flow of the process, it will happen faster and you will be 'out' (separated).
Again, from what I read, as you separate, there are several 'levels' that you have to pass through to get to a reasonable environment. As I understand it, the beings on these 'lower levels' are not as nice/civilized/kind/etc as the ones further out so these 'levels' are often where the people see scary figures immediately when separating or when partially separating from the physical body.
Of course, since I have not much personal experience, this is my interpretation of the accounts by others so take them all with a huge grain of salt and find out for yourself.