Hannah, I think that makes sense. I usually associate stress with being busy, and I'm not good at writing when I'm busy because even if I do have time, I have this guilt complex about feeling like I should be using that time for something else. But when there are other things going on in your life that you can't do anything about, writing can be a great escape. It's definitely cathartic for me, and I always feel better after I've written something I'm happy with.
I have the same problem with always thinking ahead to scenes that are so far off from what I'm writing, and then when I finally work up to that point, I sometimes have the same problem Steph brought up, where I've thought through it so many times in my head that I psych myself out and feel like I can't live up the scene I've created in my head with my writing. When it does turn out as well or better than what was in my head, though, it's pure magic.