It's a good question to ask and I understand your concern. If you were to search all the archives, you would discover a couple of people who passed really big stones. (One supposedly was the size of a golf ball, but I have a hard time believing that!)
The important thing is that many, many people have done these flushes with little or no discomfort. (except for drinking the "potions" and I have yet to hear anyone say they loved drinking the Epsom Salt and olive oil mixtures!)
So, plan a day that is good for you and flush away. What do you have to lose? (and besides, you get to keep your gallbladder!)
Paulette G.