worried about this one...

I'm 15 weeks with my second child. Throughout my pregnancy with my son I didn't worry about anything really, expect eating healthy and what not. This time around I'm terrified for some reason. I'm worried about no movement, that I'm gonna go to the dr and they won't be able to find a heartbeat. The dr just asked me the other day if I wanted the test for Down syndrome done and now that's all I can think about. My son was in nicu when he was born with an infection of the lungs. I don't know if that's causing my fears or if this is just my hormones or what. Does anyone else feel this way during their second pregnancy?