I totally just posted in another thread about sleep paralysis before I saw this!

I might as well add in my 2 cents here too.
I've also experienced this many times throughout my life, but it first started happening when I was a teenager. (As a child I had some night terrors too, apparently, but I can only vaguely remember them.) I was often depressed due to typical teenager bullshit, and because of that often pretty stressed too, so I wouldn't be surprised if that's what started it.
Anyway, I've been able to have a lot of really cool lucid dreams once I figured out how to control it, but a few pretty bad experiences as well not unlike some of the stories being told here. The worst one I've had is actually pretty tame in comparison, so unless anyone really wants to hear it I won't bother sharing... but that was the only time I ever felt truly paralyzed with fear. Even if I could have moved, I was too terrified to do so.
Since that one bad experience, I couldn't forget how scared I was and whenever I felt it begin to happen again, my mind would shut it down immediately and force me to go back to sleep so I could wake up normally, but it didn't always work. Then later in life I learned about lucid dreaming and I was interested in how sleep paralysis was related, as well as methods of learning to control it in order to use it as a gateway to becoming lucid. That changed the way I thought about it, making me want to face my fears and such, and once I learned to trust that it was all in my mind and I could see whatever I chose to see, I had no further bad experiences, only a few that were maybe slightly unusual or unnerving.
Brains, especially dreaming ones, are weird. It's interesting, all the theories about astral projection and deja vu and such, because to me those make a lot of sense, even if I am still skeptical. I read an article once where someone theorized that dreaming is actually the brain's way of preparing the body for scenarios it thinks might happen in real life, but that haven't happened (yet). Your subconscious is pretty astute when it comes to figuring these things out, hence why they can be prophetic or eerily close to reality. As a biological mechanism, it makes sense.
I also recently read up on
dimethyltryptamine (DMT). It's a psychedelic drug as you probably know, but your brain actually produces it when you sleep. I suspect it's the culprit for some of the crazy shit you see/hear during sleep paralysis, and the astral projection, lucid dreaming, etc. People often report having out of body experiences when they do DMT. I can't speak from experience, but I can recommend that lucid dreaming is awesome and if you can learn to do it, you might be able to control the sleep paralysis as well. It's more or less a process of learning to control your own mind.
I guess that's the only real advice I can offer. I know that 5-HTP supplements can help you attain lucidity (another form of tryptamine... geez, what is this stuff) but I'd be wary in case it backfires by making it more intense. Maybe a milder sleep aid, something like melatonin that doesn't need to be chemically converted? It could maybe also be
sleep apnea severe enough to cause the sleep paralysis, which in combination I can imagine would be pretty horrific. Perhaps see if you can get into a sleep clinic so they can monitor what's happening.