<human>: Could you distill the essence of the text into 1-3 sentences?

So we're hanging out 2 nights ago when she suddenly asks me "What if I get pregnant." My initial reaction is I laugh (more on that later) but then we talk seriously about it and what comes out is that she won't have an abortion but would consider giving the baby up for adoption. I told her I wouldn't be ok with that and would raise the child myself if it came down to that. Neither of us explicitly mention us raising the child together. 

So here's my real problem. Her question is not an unreasonable one as we're having sex regularly. But the situation is highly unlikely. She has a copper IUD that's good for another 5 years or so and it's probably the most foolproof birth control available. I also know she's not currently pregnant, she was on her period the previous time we hooked up about 5 days earlier. Also it would conflict with her long term life plans to get pregnant now since she plans to live outside of the country for at least a few years once her current work contract is up in a few months. So why am I left with this overwhelming feeling of dread and panic?

A little bit about me. I'm not normally terribly emotional. My initial emotional response to almost everything is to laugh, even if I think its not particularly funny. A therapist told me once its nervous reflex, but I don't consider myself particularly nervous. I'm not really prone to anxiety, and while I might avoid thinking about things when I put my head to a problem I'm usually pretty decisive with a course of action. But this. I've got nothing. I keep thinking about what I should do. My mind keep circling around it to the point of distraction. I like the brief time we spend together (a few hours, once or twice a week.) but I know we couldn't ever have a real relationship and raising a child together would be an absolute trainwreck. I also know that its nearly impossible for her to get accidentally pregnant and it makes no kind of sense for her to get herself pregnant on purpose. Normally this would be an easy thing to put out of my mind. But this time I can't and I don't know why.
<bot>: Had the "What if she got pregnant" discussion with FWB and now I'm left with unshakeable dread in the aftermath.