Stressed dieting, relaxed eating?

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So I have what might be a slightly weird pattern to my eating - I manage calories and nutrition extremely well when stressed (I actually usually have to force myself to eat and never have any appetite when stressed, so that helps). However, once I relax and get to spend time around friends again, I stop caring so much about what I eat and gain all the weight back.

Does anyone else have a similar problem, and some strategies for kind of "staying on the wagon" during relaxed times such as vacation? It's much harder for me to maintain a low calorie count when I'm constantly being invited to meals, and don't feel like I have to respond to stress by more carefully managing everything. Not to mention that I gain my appetite back on vacation.