your situation matters a lot. What continent, hemisphere, whether the house is air conditioned or exposed to the elements? Type of piano, Brand, etc. Certain high dollar brands recently built, you call the tuner and wait. An old beater, that could be replaced for $40 plus the cost of renting a trailer and a helper, you can afford to be more exploratory in the repair method. I had a sticky key on my 1941 40" console, but changing from forced air heat, which dries the house out, to heat which pumps humidity into the house in the dry winter cold spells, has mostly solved the problem for me. Don't try this in a modern house with vapor barriers, triple pane windows etc, you could asphyxiate yourself. But in an old somewhat drafty house, the hysteria about gas fumes is rather overdone.
On an old upright piano, worth nothing, that you own and could replace if necessary, you should carefully inspect the visible parts, when this happens, to see if you can see anything rubbing. Another plan is to buy the replacement upright piano before you try anything new and creative. In my part of the country they are on internet listings or floors of charity resale shops, all the time. Your best investment then, is renting a serious piano quality dolly. Rubber bolsters and 5" wheels, a 1200 lb rating.
Topic: stuck piano keys!