I've just finished reading "Astral Travel for Beginners" (after several out of body experiences with Salvia and Peruvian Torch), but I haven't been able to Astrally Project at will without the use of entheogens, I believe because I'm not quite able to let go yet. However, throughout the book they emphasize that it is entirely safe, regardless of scary experiences that you may encounter.
This morning I awoke around 5AM. I experienced a discussion with what I would describe as other beings, although I believe this is just how my human brain could interpret the information I was receiving. I was able to ask them several questions, before I started waking up too much. I definitely got the sense that I could have seen them as terrifying, and become paralyzed with fear; I had a brief glimpse of this, but I reminded myself that I would manifest what I wanted to see, and they again seemed benevolent.
From my experiences, I can't help but think that scary SP experiences are the result of confusion about the control being switched from physical to mental.
A friend of mine recently had a SP experience where she was surrounded by malevolent men, but could not reach to turn on the light, and was unable to touch the men, even though she was trying to.
I certainly can't say for sure, as I haven't had recurring SP as some people have, but I have had several lucid dreams throughout my life that have left a big impact on me, and I believe that they could have been terrifying if my consciousness didn't realize that it wasn't reliant on my physical self, and was free to explore.
This may sound like a judgement, but thinking of it as "sleep paralysis" to me indicates a fear, or a negative connotation, or a struggle between mind and body. Perhaps the wonderful liberation of astral travel is a hellish torment when the astral traveller finds her/him-self trapped within the physical.
Someone was saying relaxing makes SP go away more quickly; could these experiences be turned into powerful, enlightening experiences by letting go of fear of losing attachment to the body, and letting your consciousness be freed of your body? To me, this really seems to tie in with Buddhist ideas of letting go of your fears, especially the fear of releasing your consciousness from your body.