C.D.
It's hard to say exacty why this is happening to you. I feel for you, I know how horrible dreams like this can be. Dreams come from our subconsious mind and so there may be hidden fears within yourself that are coming out in this way. Even though dreams are of the mind, the body affects this and it can be something you're eating especially if you're eating at night. Could be hormonal. Maybe you could try putting on a Cd of soothing music, waves, rain sounds, etc., or positive affirmations while going to sleep. Thats what my sisiter did and it changed everything. She put on a CD that had low soft music in the background and a soothing voice that repeated affirmations like, "I will have a calm loving birth", etc.
Hope this helps
The very Best to you and your wee one, I hope all things are better for you and you have a loving, empowering birthing process