It's fun seeing how much weight I can gain in 24 hours

One time I put on more than 10 pounds in a single day, just to play around and see how much variation is possible in body weight in a short time period.

I started out that morning pretty light, having used the bathroom and not eaten much the day before. I ate a normal amount of calories, going to about 2,500 which was my TDEE. Then, over the course of a couple of hours, I drank as much water as I possibly could. It was really uncomfortable near the end, but I stuck through with it and kept drinking...I went up from 147 pounds to 161 pounds in one day. I was pretty proud, haha. I didn't really do it to prove anything, just to see how much I could gain.

Anyway, in retrospect, it did make me realize that your body can change weight very quickly without any lasting effects. Obviously my weight went back down very quickly because all that excess water left my body soon enough. Everyone knows that--it just feels much more concrete when you try something like this for yourself.

In the short term, gaining weight is not always the result of consuming calories. Often, most of those extra pounds you see on the scale are because you might have eaten something heavy in weight but light in calories. In the short term, weight gain =/= fat gain, so don't panic if you gained five pounds on Thanksgiving. You can't gain that much fat even if you eat 2,000 calories above your TDEE. Long term trends in weight are important. Short term changes are most likely fleeting.