Sleep paralysis is definitely a real condition. It happens and has happened to me a few times, in jail oddly enough. Most all of the research is theory though. Never been any definitive answers as to why it happens or how to stop it. It has nothing to do with the DMT produced endogenously within the mammalian brain. DMT has also never been associated correctly with REM sleep patterns...
What I do know from personal experience is that SP only happened for me when I slept on my back. Rather I might say that I 'woke' up laying on my back. There was an incredible pressure pushing down on my rib cage and chest area. My eyes seemed open and I could hear and process much of what was going on around me at the time. Yet I was unable to move and speak. It felt like my brain was sending signals to my limbs- 'move, sit up'. You know, but they weren't being received properly. Then at some point my nervous system snapped out of it and I was up, thinking 'the fuck is this? The fuck was that?'
Total confusion, even though I had heard of SP before. As I said earlier- SP has happened to me just a few times and all three of those incidents occured during an extended stay in Santa Rita Jail. During this time I was dealing with a lot of stress. And my sleep patterns were as fucked as they had ever been.
Also, the Asian guys I was locked up with had an interesting take on the whole sleep paralysis phenomenon. We got into the discussion over a huge bag of pruno as I started explaining some of the scientific reasoning behind SP, all of them cut me off at once and they began basically telling ghost stories. Claiming it's spirits. Eastern philosophy type shit.
One OG Cambodian said it happens to him all the time. Over the years he learned to control it and can now basically lucid dream at will. He said to me "You ever get stuck like that again, just wiggle your toes!" I took it as good advice.