I sometimes get what I think you're describing where I wake up from a dream and get a sudden feeling of terror, but this isn't sleep paralysis.
I had a single instance of sleep paralysis when I was a kid. I was extremely stressed out because I'd been feeling rather ill for a good few weeks.
I remember having spent an entire week and a half on the couch; standing up for more than a few minutes would cause me to get dizzy and extremely nauseous.
One afternoon during that period of illness (which was likely due entirely to a stress disorder I realized I had later), I was taking a nap in bed, exhausted from being sick and doing nothing.
I woke up from my nap hearing my name being called. It was strange, because I didn't recognize the voice, but the voice was very distinctly talking to me.
It's like how someone can call out to you when you're not even looking in their direction, but you sense and know you're being talked to.
Besides that, this voice called my name.
So I looked across the room and down the hall. The voice called again and again, so I called back asking, "Yes? ...Yes?"
Suddenly, the voice was in my right ear. It startled me and I was frozen in fear--I was alone in the room and this person calling to me hadn't entered from the hall.
I distinctly remember the chill that went from my skull and down my spine.
The voice, now whispering my name into my ear, was so close I could feel the breath against my face.
This is where I was so scared, I probably would have shit myself had I not been so terrified that my asshole had permanently closed shop for the day.
I remember trying to leap out of bed and get away from this entity speaking to me, only to discover that I was unable to move. Totally unable.
Being paralyzed is a strange feeling when you're consciously aware that you shouldn't be paralyzed.
Most of us are fairly twitchy all day. Whether we're tapping out foot to a tune, rapping our fingers, twiddling our thumbs, etc.
This feeling of being paralyzed is, in part, so terrible because your body isn't even subconsciously able to move in the slightest.
It's really similar to the eeriness of being in a pitch-black cave that is entirely, completely untouched by sunlight, and deafeningly silent.
Stuck in bed with a voice whispering my name into my ear, unable to escape, and scared to the point that I became temporarily mute, I felt the fingers dig in.
Four fingers grasped both ankles, and the thumb slowly squeezed around the Achilles tendons.
I felt my ankles being forced downward into the bed, held down. Try as I might, I was unable to break free of that grip.
The voice again called me, this time from the foot of the bed.
I tried to kick free, but my legs wouldn't budge, and the hold on my ankles became painfully tight.
At that point, I felt two palms press down on my chest. Again, another whisper.
The palms pressed down on my chest so forcefully that I heard the bed creak from the weight. I was being suffocated.
After a minute or so of the attack, it seized, and I quickly sat up, still frozen from fear.
I got up and went downstairs, told my mom what had happened, and, after a few hours, carried on with my day on the couch, sick and now also afraid for my life.
Anyway, sleep paralysis is bad news and it fucking sucks and I hope none of you ever have to deal with that shit ever again.
Idk if this is at all related or not, but I've had a couple occasions where I woke up and hallucinated creepy shit... no paralysis though.
First time:
I was maybe 6, and my room has just been repainted (to a sweet color called "gecko green." I was 6, gimme a break), so I was spending the night on my brother's floor since the paint was still drying. I woke up at 3 or 4am in the morning, with an odd sense of dread. I sat up a bit, propped up on my elbows and looked out the door of his room. Normally from his room you could look down the hallway and see my parents room's door as well as mine on the other side and down the hall a bit more. Instead, what I saw was the backside of a fuckin stegosaurus monster or some shit. It made absolutely no sense, since something this big couldn't have possibly fit in the small hallway there. Regardless, being 6 and seeing this thing clear as day walking away from my bro's room and down the hall towards mine was enough to make me just slowly lay back down and pull my sleeping bag a little tighter as I mentally convinced myself that couldn't have been real. Only then did I roll over and see my brother staring wide-eyed at me, looking as startled as I probably did, before he slowly laid back down as well. I should probably mention that the scaly-leathery skin of this beast just so happened to be the exact same shade of green as my room.
Later that day, after I finally fell asleep and woke up, I asked my brother if he happened to be awake early that morning as well. He simply said yep in a shaky voice, then walked outa the room, kinda avoiding further prodding... I never did ask again what exactly he did/saw at that hour...
tl;dr: Inhaling green paint fumes while you sleep makes you hallucinate green dinosaur monsters.
2nd time:
So this time happened a lot more recently, maybe 3 years ago, during the summer. My neighbor and I were out walking around the neighborhood late one night, maybe 10:30-11. During that time we saw a fox/coyote at the very edge of our vision a couple times over the course of our ~1.5hr walk (which is a relatively rare sight in my area). The thing was, this wasn't a nice and cute little fox thingy... not at all. From what we could tell this was a mangy, feral, rabies-spreading beast. Its fur was all shaggy, it had scrawny legs and its whole body was little more than a skeleton. The would-be-bushy tail was all wet and matted, or something... maybe it was missing some hair, who knows. Either way, not exactly the type of creature you would want haunting your nightly stroll.
Now the thing with this mangy mutt was that all of the times we saw it, it inexplicably disappeared. First time we saw it, it noticed us and then walked from right to left towards a dark tree.Then it never emerged from the other side. My neighbor and I went to investigate thinking it might have a den at the base of that tree or something, which could be neat if we had fox pups running around the neighborhood later on in the summer (needless to say we didn't get the best look at it at this point, and before it vanished we had yet to brand it a demonspawn, so cute little puppies seemed possible). Second time we saw it much more clearly since it was at the end of our road, right before a hill. At the base of this hill was a house that had some yard lights on, so they lit it up real nice. What we saw was one of the most haunting silhouettes imaginable. It started to walk towards the curb, then hopped up onto this houses lawn and started to ever so slowly disappear from our vision as it went down the hill. My neighbor and I were really close, he was scared as could be and nearly petrified, so I oh-so-bravely strode up to the hill to investigate. Despite walking into one of the most barren lawns imaginable (can't really put much on such a steep incline, I suppose), this demon was able to vanish entirely. Needless to say we were both more than a little spooked at this point once I broke the news of my discover to my neighbor, so we called it a night.
But the tale doesn't end there. Later that night (well, probably more like sometime very early the next morning) I finally fell asleep, only to have a pretty strange dream. I was randomly a part of some sort of taskforce that was tasked with capturing someone's lost pet (a cat, maybe?). Pretty odd stuff, but whatever, dreams are dreams. So we all split up (don't even know who the "other people" were, just kinda knew there were others) and after a while I realized that hey! I was walking around MY neighborhood. Things started to get kinda freaky when I noticed myself walking towards the end of the road and found myself looking at a silhouette in the dark, illuminated from behind, yet again. Only this time the silhouette wasn't all that frightening, and as it turned away I ran after it, burlap sack in hand to capture it (lol, dreams are weird). Somehow, I was apparently fast enough to catch up to a sprinting animal, so I pounced on it and threw the bag on top, capturing the rascal. Next thing I remember I was meeting with all the other "people" again when the thing starts throwing a hissy fit and begins struggling in the sack like mad. Apparently I didn't tie the bag shut or anything, so I ended up dropping it and then it jumped out of the opening, right at me. Cue waking up in a panic before I could actually get a good look at it or get slaughtered by it, or both. So I've got this impending sense of dread again, and as I roll over in my bed I see a fox/wolf/coyote hybrid (with a little bit of deranged monkey thrown in there somewhere) floating over my feet like some sorta ghost. I bolt upright and begin shaking my sheets at it, pretty much automatically. Don't ask. So as I'm shaking out my sheets at it, I of course end up knocking shit all over and making a mess, but whatever, scaring away vile fox demons that had been haunting me all night long kinda took priority. Eventually it just kinda fizzled out, and all was quiet again. It probably took me several hours to sleep again after that, despite being waaaaaaaay overtired already, and it was definitely one of those instances that really make you wonder...
tl;dr: I got haunted by my friendly neighborhood demonspawn.