FWIW, my third pregnancy happened more or less the same way (we were on the fence, decided to chance it and have unprotected sex exactly once, and I got pregnant). I definitely had a "WTF were we thinking" reaction at first, but #3 is the best thing ever, and I am SO glad the decision was more or less made for us, because I am not sure we ever could have gotten 100% there on our own.
I think you will end up being SO happy that things worked out this way.
This is weird, but I had a strong feeling you were after you posted about the times in Napa. And fwiw from an Internet stranger, I have a good feeling about this pg for you.
Congrats! I'm glad the decision has been made for you!
How did your H react? Did you tell your family yet or are you going to wait?