Hi Honey. I'm so sorry for your earlier losses. This kind of dream is completely common. It's your anxiety and worries working their way out in your head. I kept having awful dreams about my baby when I found out I was PG (Including Aliens abducting me and taking my LO, a double whammy for me as I have been scared of Aliens since childhood!!)
Everyone used to tell me to calm down, and that it wasn't good for the baby to be such a stress head, but it is easier said than done. Do you have anyone you can talk to about this? Even your MW or doctor? I found talking about my fear and getting it out of my head helped so much. I still worry, but I am a lot more relaxed and my dreams have shifted from nightmares to .... well let's just say they are not PG rated!
Focus on the good things, you've seen a scan, the heart was strong and everyday is one more step forward. Try and have a good talk about it with someone who will understand and let you work all the fear through and wont just tell you to calm down.
I think people's minds are very good at grabbing hold of our fears and pushing them forward. I remembered thinking my brain was preparing me for losing the baby (We've tried for 4 years and this is our first).
There are good things to help you relax, milk is great, simple I know, but it does contain a mild relaxant (Which is why people recommend it before bed). Chamomile tea also can help you stay calm and it is safe during pregnancy.
Focus on the good things, honey and take it one day at a time. If you have a bad dream, in the morning, take five or tea minutes to think about it then say "Right, it was just a dream, I feel fine. I'm going to do this today....... (Insert busy work to keep your mind off it)".
Hope I've been a help. xxx