Edrick, This is quite normal in sleep paralysis (SP) and it's nothing to do with the supernatural! I can speak with some authority on the subject as a former neuro nurse and, more importantly, someone who's had SP with all its attendant hallucinations for 50 years.
I'm sure you know this already, but for the benefit of anyone else reading my post, who might not understand, this is how it works. During the REM (dreaming) phase of sleep our brain secretes a chemical that paralyses our voluntary muscles, for the obvious reason that if it didn't, we'd all be running around acting out our dreams. In a tiny handful of people, the chemical doesn't get secreted and they do indeed act out their dreams, but that's another sleep disorder, and fortunately a very rare one.
In the much more common SP disorder that both of us suffer from, the brain either starts secreting the chemical before we're asleep or carries on for a minute or so after we wake up. In some people it stops there. They wake paralysed, then manage to move after a few seconds but with no "special effects".
Some of my SP episodes are kind of vanilla-flavoured like the above, but the majority are more like yours. Unfortunately, hallucinations are very common in the SP state, and they can affect any of the senses. Mine are mainly tactile but sometimes have auditory elements. My father's affected just about all his senses. He often saw very unpleasant things and smelled them too. And yes, SP is strongly hereditary. My father, at least one of his siblings and my grandmother all had it.
I can see from your post that you basically understand that you're not being attacked by anything scarier than your own unconscious - though I realise that's quite scary enough! In addition to having SP myself I've been in a lot of contact with sufferers on-line in the past, and it's always struck me that SP hallucinations (including mine) are far more likely to be unpleasant than enjoyable, though there are exceptions. I've come to the conclusion that it's our instinctive fear of what we perceive to be "the other" that makes them so frightening. Even now, when I'm well aware that I'm only being mugged by my own unconscious, I can still react with fear in that first second when the hands grab me (or whatever) and the fear is enough to cause the whole thing to turn ugly.
Before I forget, that deep groaning you heard was probably you, even though you might have perceived it as external. As I get older I've started to snore, and I've noticed that more and more of my SP hallucinations involve growling dogs! However, I also occasionally hear noises that clearly haven't been physically generated by me - mostly just running footsteps and, for some strange reason, taps being turned full on. Maybe I was traumatised by a running tap when I was a child!
There are all kinds of strategies for avoiding these attacks, and getting out of them once they occur. The most important is to identify your triggers. My main trigger is getting overheated in the night. I also tend to get SP at times when I'm sleeping too much, or if I drink a glass of wine too many in the evening. And stress is a good all-rounder too, of course. In fact my first ever SP attack came in the run-up to my nursing finals. However, everyone has their own triggers. Getting over-tired can be one, smoking weed, over-stimulation in the last hour before bedtime (e.g. gaming), sleeping too near an electrical junction box of any kind or under high-tension cables. The last one might seem surprising, but neuroscientist Michael Persinger (google him) has postulated that it's an electro-magnetic phenomenon, and has even been able to replicate some of the effects in the lab.
To get out of an attack, concentrate hard on the real position of your body, which can be harder than it sounds because of the nature of some attacks, and try to wiggle the last joint of your fingers or the tip of your tongue.
I've also learned over the years to talk to my "attacker" - which is, of course, just another part of me. When I say talk, I mean mentally as it's quite difficult to produce a sound while paralysed. Getting angry and shouting at "it" is seldom helpful and usually makes things worse. Some people find it helps to calmly ask: "What do you want?" In more recent years, I've discovered that it works better if I reassure this other bit of me. I now say: "It's all right, I like you". A psychologist once told me that this indicates that it's the Freudian id (google again) that's at play here, as this is a rather whiny, needy part of our psyche.
Finally, you can go to your doctor and ask for antidepressants. They suppress REM sleep so will completely stop your SP attacks. I gather this is how most people deal with the condition these days. Each to his own, but I personally think this is a pity. For one thing, antidepressants can have some nasty side-effects and withdrawal from them can be difficult. And in any case, SP is very manageable once you get used to it and understand yourself.
Most people find the frequency of attacks declines with age, ditto the severity. This has certainly been my case. Now, in my 70s, I only have two or three attacks a month, and most of these are very brief and don't involve hallucinations.
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