Once, when she had just started trying foods, my daughter woke up from a nap spitting up in a different way than I had seen before. Instead of just cleaning her up and moving forward — as I’d done so many times with my son — I became untethered: I was sure this was the end; that she’d throw up again, and again, and then be gone. Because of my work, I knew the way little things like this set me off was emblematic of PTSD. I also knew it was changing the kind of mother I had been to a more hesitant and worrying kind.