Some of the research on FODMAP sensitivities actually talks about how the anxiety/expectation that you will get sick, causes you to get sick, or more sick then you otherwise would. So it's partly in your head, true. But that doesn't make it any easier. It's really, really hard to control your body with your mind, especially when it DOES physically make you somewhat sick, and then your mind/anxiety makes it worse. Saying this is true, doesn't make it any easier really.