one question

Not convinced. Another thing i'm not convinced about, though, is whether inflation potions are completely imaginary. I don't mean a spherically inflated person, but if you can either preserve nucleation sites in the stomach with carbonated water or find a safe way to react a carbonate and an acid in the stomach, you definitely would get a release of a very large volume of gas. Diet coke and mentos being an example. The problem is getting it to happen inside a human container without harming that container.

You can get 100 litres (22 gallons) of carbon dioxide out of 160 cubic centimetres of calcium carbonate combined with the appropriate amount of weak acid. That's way beyond the safe capacity of the human abdomen, so you'd have to be careful, and another issue is the safety of the compound produced along with the pH of that compound. But it does mean that the physical result of swallowing enough antacid tablets with, say, citric or tartaric acid, will cause a lot of bloating. It wouldn't be safe, mind you, but physically speaking it is possible. The problem is safety, not whether it can be done.