Caution - tl;dr
Anywho, my wife suffers from this from time to time when stressed. They used to terrify her but this is something that once you understand what it is, it becomes a whole lot less scary and sometimes downright entertaining.
A few examples
- once she woke up to what appeared to be a monkey sitting on her chest. Every time she tried to lift her head to look at it, it would push her head back down. She said it would have been cute it it weren't so mean!
- another time she woke up to see the ceiling fan in our room glowing and spinning so fast that she was pressed against the bed and couldn't move to somehow try to turn it off.
- then there was the time that "Gandalf" from the LOTR movies came in and sat on the side of the bed staring at her as it trying to figure out "what she was exactly"
We are actually entertained by these, but a few nights ago she had what was probably the most detailed and creepy one ever:
She's laying there on her back, just drifting off to sleep when she hears a scratching noise, then something walk into the bedroom (this is almost always how they start..)
As usual in these episodes, she can't move, but from the corner of her eye she sees a shadowy, absolute black figure enter the bedroom. It's kind of poking around the room as if investigating. She's able to see it full on now and it's a pitch black shadow in a human shape, but as she blinks, she can actually see a person as though her eyelids are some sort of "filter". She closes her eyes and "looks" at it and sees that it's some sort of "revolutionary war" type soldier. "He" has long messy hair, and wears a blue and black uniform that is very disheveled and beat up as though he just came back from a battle. He spots her looking at her then acts startled, walks up to her and leans over her staring at her face from about an inch away (freaking yikes!!!). She says that he seems perplexed that she can see him and is examining her intently. Somehow he seems very authoritative like some sort of officer or leader of some sort. She hears him say something but it's in a different language and she could not understand. He/it waits for a reply, but she doesn't respond so it kind of backs out of the room and is gone at which time she could move again...
This one would have been routine if it were not for the fact that she described a Hessian soldier without actually knowing what one is! Freaking awesome!!

(we live about 15 mins away from the site of the Battle of Trenton, I keep on spooking her that she met a bonifide ghost who had wandered by in his ghostly travels)
No, it's not a ghost story, but it's amazing how the subconscious mind can store info then reuse it without the conscious mind realizing.