Stress, weight, calories

melanogaster

Ok, this is probably a dumb question. I understand the basic mechanics of weight loss pretty well... weight change is the difference between calories in and calories out. Got it. But... when I'm under extreme stress, my weight goes up, usually a couple pounds, and fairly quickly. Even if my calorie intake has stayed the same, and if my daily exercise hasn't changed. And then when the stress goes away, like magic I'm losing a pound a day (I'm aiming at losing about a pound and half a week, so this is a pretty dramatic change). This has happened enough now that I can say, confidently, that it's clearly connected to my volatile relationships with certain of my family members.... but, why does this happen? Not why do they stress me out (I know that), but why does that stress make me temporarily gain weight?