A bit late but...
I think that most dreams are just the detritus of the mind, the random images and thoughts that pass through our subconcious based on the things that are happening in our life, our emotional state, past experiences etc. But, and this is a big but, some dreams do not appear to fall into this thread.
I have extrememly vivid dreams, so vivid that if I fall in love in a dream, have a child or someone dies I will sometimes cry/mourn for them when I am awake because it feels that real. I dream in color but also in 'feel', 'taste' and 'smell'. I almost always remember several dreams a night and can actually lay down and as soon as I fall asleep start dreaming. I am also extrememly sensitive to what goes on outside me, IE if the television is on I will dream what is happening on TV word for word, so I have to be careful of things like that (imagine falling asleep during a scary movie...).
Some of my dreams are horrible and unlike most people I do not wake up just before I am tortured or die etc. I actually experience the entire thing including the pain. Some dreams are so real that I will actually take action. For instance I once dreamt that I was a priestess in training and that these half man half snake creatures were chasing me through a moonlit forest. I stumbled into a clearing and was surround, tied to a stake and then tortured. The snakemen dips wands into boiling wax and rolled them down my arms and legs peeling off the skin. When I woke up I was covered in blood because I had torn all the skin from my arms with my own fingernails trying to stop them. To this day I cut my nails as short as possible. You would think that kind of pain would wake me up but it doesn't. Iv've had dreams so scary I bit right through my tongue and I still don't wake up.
Sometimes I dream of past lives. Many people don't believe in that and it's ok but I have no other explanation for the very intricate and lengthy 'lives' I live in my dreams nor for the intense feelings of attachment and rememberence I feel to them. Some of my dreams are so detailed I have actually made them into stories and am currently working on a novel based on one of my dreams. I have had several dreams that have come true, usually very silly things (I always dream about the place I will live next before moving) but occasionally something more bizarre. For instance I once dreamed about a little girl who died and the next day it was in the papers. I usually have no control of my dreams even though I am aware it is a dream but sometimes I do. I remember once when I was little and I was dreaming of being chased by zombies. I stopped in the middle of the road and told myself 'This is just a dream, you can do anything you want' and proceeded to fly away. At which point the zombies started laughing and said well its our dream to so we can fly to and chased me through the sky.
The condition you are refering to is sleep paralysis. I had a big problem with it when I was a teenager and seriously thought I was either going crazy or being abducted by aliens. Before modern science figured out it's cause people used to believe it was demons sitting on thier chest and holding them down, IE the succubus. Here is a good site with more info:
. I think mine was due to stress because I had a very hard life and stopped having this problem after I left home. When I was very little I could leave my body at will even when I was awake but I can't anymore and wouldn't even if I could. Still sometimes I do get that feeling where I am almost asleep and then suddenly jerk back and feel like I am falling very fast. Maybe my soul wants freedom even if my brain wants safety.
Most of my dreams are the same common dreams everyone has, running down a road that gets longer and longer, being naked in front of your class, etc. But some defy logic. I guess I should not be surprised considering the other bizarre things that happen to me and my mothers even wierder sleeping habits but it really is quite strange. Good luck and blessings, Prana