Another often overlooked reason for seeming to gain weight overnight is the fact that
bathroom scales are hideously inaccurate!

Those things are ALL stamped "Not legal for trade" somewhere because they cannot be trusted. So don't get hung up on a difference of a couple of pounds from one day to the next. It could just be the way you stepped onto the scale: faster, harder, slower, more gently, toes on the frame or not.

If your weight is different from one Monday to the next, then begin to think that maybe you might think that you have gained or lost. But as Nat has often said, the way your clothes fit (the famous Pant-o-meter) is a FAR better gauge of how you are doing.