I was wondering, as I was reading your post, if you'd ever considered demonic oppression. For many year now I've suffered, not from sleep paralysis, but from insomnia. I'm not suggesting that it is that, but it's an avenue worth considering.
Just to outline my insomnia for context. For many, many years now I've suffered from insomnia. It's usually been cyclical, with periods of sleeplessness or shallow sleep, followed by periods of being able to get a few hours deep sleep. Rarely have I had what I'd call refreshing sleep, just relatively better nights. Last year was a strange time for me. Out of the blue I started sleeping well. I even slept well away from home, which has always been a problem for me. Then, in October last year it suddenly ceased and since then I've had the worst insomnia of my life. Last night being a typical night. I went to bed at 10pm and, as I usually do, started reading a book. I didn't put it down until gone 2am and only because I thought I'd better try and sleep. After 5 hours of tossing and turning, with very light hypnogogic sleep (it's a dreamy state where I feel I can wake up at any moment if I choose to) I was up again, thinking it's pointless to lay there any longer. In 2019 I could read more than a chapter before feeling so dowsy, so deeply relaxed, I had to just put it down and sleep.
This is the weird part. Why I mentioned spiritual warfare was because around 2015 I started to experience what I'd call ghostly, nighttime visitations. It's difficult to describe in words, but I'd sense a presence around me that whispered and moved up and down my body touching me. Not a physical touch, but let's say an ethereal, ghostly touching. When laying on my side it seemed to approach from the rear oftentimes and, although I did not get a strong sense of evil, I did think there was something sexual, which freaked me out. So I'd lay on my back and pray. When it became persistent and scary I took to leaving the light on. Then, at the end of 2018, I decided to look for a priest. In the UK I could not find one Catholic priest, but I did find that Poland had many. So, since I'm half Polish, I flew to Warsaw. Long story, but I did not make contact with that priest while there, but I did have what I'd call a spiritual experience of sorts in a church I visited. I was praying and just started crying. I realised that I was grieving my father's death. He was from Poland and died in 2014 and I had never grieved his passing. My period of sleeping well commenced around this time.
On my return home, the visitations became less intense and gradually stopped. I should add that around the same time I started to practice the Jesus Prayer and have been doing so ever since. Now I no longer get the visitations but I still feel a sense of spiritual oppression or at least activity, which is a little too complicated to write about here. Sorry to write so much that isn't exactly related to sleep paralysis, I just thought that, as someone who used to experience sleep paralysis frequently, I have also had some pretty weird spiritual experiences and that the two might be related.