There is no weight gain from gas (they eliminate the gas they use when the surgery is over, plus gas has no weight). There is often "weight gain" because of all the IV fluids they give you in the hospital, however. It can take anywhere from just a couple of days to a week (perhaps even more, I suppose, depending on your own body) to get rid of it.
10 years out; 190 pounds lost, 165 pound loss maintained
You don't drown by falling in the water. You drown by staying there.