Baby dreams.. or nightmares

I keep having these dreams... well nightmares really. They're great at first, I'm 21 weeks pregnant & then I start freaking out that I'm miss-carrying. I have only been pregnant once& didn't find out the baby had died until three weeks after and had to have a D&C; at 11 weeks. I had all the "healthy baby" symptoms & my doctor was even confused but we moved on. We're now actively trying to conceive but these dreams are making it so hard to try and get pregnant because it's like my heart wants to but my mind is putting up a wall so I don't get my hopes up again. I hate this. How do you stop the constant heartache even when you're asleep!