I've interpreted about 6000hrs of sleep recordings and have been co-author on publications in sleep medicine (albeit not publications on sleep paralysis). I have not worked in the field in a number of years but I do keep up as a hobby. I'm probably the closest thing to an expert on sleep paralysis this sub has. (I've also experienced it myself, multiple times, though it's been about 8 years since the last time. I should note that I don't in general believe sleep paralysis to be supernatural not believe that mind was.)

The other poster is correct in pointing out that this is a hypothesis. Quite frankly it's a guess. That guess is very informed-- REM sleep does typically feature paralysis, we do know of hypnagogic/pompic hallucinations, it's reasonable to assume sleep paralysis is a failed combo of the two-- but there is little to no confirmatory evidence, largely because it's difficult to find a good way to measure it.

Consider that sleep paralysis is a sporadic occurrence, one that we do not know of any reliable way of inducing. Sleep laboratories are expensive and the prep for sleep studies is a pain in the ass (for the patient). How long do we do this before someone has sleep paralysis?

Second, there although REM sleep is often characterized as "dream sleep", you can dream in any stage of sleep. Or rather, if you wait for a given stage and then go wake people up, they sometimes report having dreams no matter what stage they were in, and even if they've had no other stages before being awakened. They report this more when awoken from REM, but it is not prima facie obvious that dreamlike experiences such as sleep paralysis must in fact be a product of REM.

Which leads to: third, of the tools commonly used in assessing sleep for research and clinical applications, it is impossible to know for sure, externally, that is dreaming. Your brain waves simply don't reveal this, and we know of no way of extracting information from them.

This is important because perception of time is distorted when people sleep. Everyone has had the feeling of waking up disoriented with no idea how long they have been sleep, or experiencing a dream that seems to last for unimaginably long times: days, months, even years.

This is a problem because even if we could find a reliable marker for sleep paralysis, we don't have any way of knowing for sure that the episode corresponded with dream content (which is what most theories about sleep paralysis suppose is occurring: the inappropriate persistence of a dreaming/sleeping state into the waking world, a mixed state).

Sure, we can ask people if they have had a dream, but we don't know if that dream occurred before and during paralysis or some other time during their sleep period. People frequently report perceived 'long' dreams even when they are asleep for less than a minute (which is interesting in itself!).

Besides, scientific theories of sleep paralysis pretty much presuppose that patient's account is not reliable. After all, if you ask a patient what's happening, they give stories like, "I was being tormented by a demon." If we don't believe they can give an accurate account of their experience, why should we suddenly believe they can accurately confirm whether they were dreaming just before, or while, experiencing paralysis? There doesn't seem to be any warrant for accepting this explanation just because we think it the correct one.

Finally, we should be clear that science simply does not accept (and cannot address) supernatural theories of causation, even if such things exist. (Obviously, this is even more true if no supernatural events can or do exist.)

Science will never accept a patient report that they are demon haunted, if for no other ultimate reason than science can only deal with direct and physical objects and events.

At best, science might say we currently do not know of a mechanism by which to explain a phenomenon, but believe me when I say that science would run through every single possible physical reason, no matter how farfetched, and in the end would conclude that the event was unexplained rather than supernatural. For the record, this is how science should work. It's a product of the methodological naturalism, a metaphysical underpinning for the scientific method.

Andddddd....this is already far too long.

Let me be clear that I am not suggesting that sleep paralysis must be paranormal because the scientific hypothesis about it is unconfirmed.

I don't know why, but people frequently seem to believe that if you deny or question one thing, it's because you believe the opposite. If I here argue that our scientific hypothesis on sleep paralysis is inadequate, it's because I must believe that sleep paralysis is paranormal. I do not, not even for my personal cases of it. I simply have no opinion because the evidence is inadequate, and I am arguing that the evidence is inadequate because it is. Not to justify some other belief.

So in summation: please don't talk about our hypotheses as though we know they are true, or that they are proven, or as though this were simply a case of wrapping up small details. We do not know what sleep paralysis is. That our guess is reasonable does not make it more than a guess; a good guess is still a guess.

I can say more on sleep paralysis because I think it's interesting but this is already too long. Thanks for reading.