I have been having really stange dreams too. Like the other night i dreamed i had to breastfeed my cat but she tried to scratch me and ran away and i felt like such a failure! I also dream often about zombies. Dreams are just that, dreams. If you let them affect you in waking life then you are mentally shooting yourself in the foot. If you have been through labour three times already then you know how strong you are and that you can survive it again.
When you wake up after a nightmare, try and think of something that you find hilariously funny. Even if it doesn't make you laugh outright, it will dispell the icky feeling leftover from your dream. I know that thinking about breastfeeding MissKitty now makes me smile because of my crazy preggo brain.
Good luck and try not to let them bother you.