I'm sorry you're suffering, but I'm SO glad it's not just me!
I've been like this ever since I had my son, and it got a LOT worse when I was pg with my daughter. So far this pg, I feel like a pretty "normal" person, but we'll see...
I also have "thoughts" when driving in a car, or fears that I'll "forget" my child in the car...basically anything I see or read in the news becomes my new freakish worry.
This is a little different, but similar in that I turned into pretty much a FREAK worrying. When I was 6 weeks pg with my daughter, I saw a news story where a local 24 yr old girl - Mom to an 18 month old boy already - gave birth to her daughter - and died. I won't even say what the condition was, because no one else needs to go through what I went through, but I googled that sucker almost every day the rest of my pg, and was almost convinced it would happen to me. That led to googling about maternal death in general, etc. I was C.R.A.Z.Y. My husband would get just pissed at me, but I couldn't help it, I was obsessed.
I've felt similarly worried about my infants as well, and also have the AngelCare monitor and that has been helpful.
Now, what REALLY REALLY helped me was MATTRESS WRAPPING. Go Google "New Zealand SIDS study." There's LOTS of information out there on it. They discuss their theory on why SIDS happens, and while it's not "proven" - it's enough for me, VERY compelling evidence. (Not one baby has died in many years in New Zealand on a wrapped mattress.) I wrapped my crib mattress, and I tell you NOTHING else has led to better sleep or more peace for me. Google it and maybe it will help you feel better about that one thing at least! (The wraps are not that expensive, they basically keep babies from breathing in molds/fungi/gases that form just above the mattresses, this is related to fire ******ant chemicals in the mattresses.)
It sucks to not be able to be in complete control all the time, especially in regard to our precious babies.