Congrats Baby Dreamtime & sammiejam
I think being positive helps our own frame of mind and the way we percieve things in our life. I doubt it does much physiologically though.
Sammiejam, given your experiences it's no surprise you feel this way. I hope you are able to get past this and enjoy a happy & healthy pregnancy. I think for me once I felt movements I was able to relax a bit, but what really helped was realising that the worry would never really end unless I let it. We get past the first trimester, then we worry about the 20 week scan, and then the birth, and then those early days, and then....
But no, nobody can be mary sunshine all the time .