I have to go back to work but I know people this has happened to and I had nightmares like this and after I've woken up. I know it is more common then what we know. Ussally this happens between 2:00 and 6:00 in the morning also. I highly doubt a doc can actually explain it. It's a terrifying exp. Sucky part of this it also ussally happens when people can be depressed. I honestly can say it was the most terrifying thing I've experience.
Fox fire. Message me.
Doctors can't explain it. Dreams themselves are still a widely unexplained phenomena, so experiences like this are even more mysterious.
As I understand it, the body has to release a specific neurotransmitter to paralyze the conscious connections between mind & body. When this neurotransmitter doesn't do its job or does it too well, for various reasons, you get sleep paralysis, sleepwalking, etc.
On the subject of dreams themselves, they serve as safe simulations of everyday fears or situations. A lot of nightmares have to do with humiliation/failure (nudity in a public space or a test you haven't studied for). Others help you solve problems by doing a deep simulation of the real world without distractions. This is why many artists, inventors, scientists, etc. come up with ideas in dreams. It also explains why sleep is essential to the learning process. You need those dreams to rerun what you learned during the day, otherwise those connections might get lost.
The rest of sleep is merely a debugging process to ensure the brain functions properly and has been cleared of excess neurotransmitters. Without it, you hallucinate, get cranky, and eventually just get so overwhelmed with neuronal errors that you can't even perform basic bodily functions properly.
Hippie Warrior

Doom War Stats: 18 offensive wars, 2 defensive wars, 38742 damage dealt, 27670 damage taken, all with 0 tech