It is different for everyone. I know about the sudden pull-over and vomit situations. It took me ten years almost before I could eat animal protein again, and surprisingly he first thing animal wise I could stomach was a hot dog. I still get on rare occasions that on the floor fetal position pain and know there is not a lot that can be done, I just had to deal with it. The only thing I found to settle my stomach was a particular beer brand and to sip on one bottle for the next 3 hours. The only time that I drink a beer lately is when I need to use it as medicine and not pleasure.
There can be a host of things that go wrong and cause gut problems, trauma physical or mental, or parasitic invasions. What works for one may not work for another, so it becomes a trial and error thing. All I can say is do not give up, you may always have some issues but finding something that can help alleviate it is a big boon.