Well, I think constantly checking your BMI may fall into the category of worrying a bit too much about your weight. :>) I have been obsessed a bit with my weight too and it's easy to get caught up in. I think though, in general, a lot of people do lose weight when anxious or nervous. That's not too unusual. We are less hungry and with fretting sometimes comes more movement. When I'm relaxed, I eat more. I think trying to maintain stable mood is the best answer here. Not so much that anyone can have a stress free existence but looking for triggers and working on them to lesson them and if anxiety is of a level that it is commonplace, talk to our doctor about it is probably best. Anxiety is treatable. And eating disorders are under the anxiety disorder umbrella. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5558599/