It’s all in your head. A simple and old saying, however it ignores the weight of our mind. Mental issues are not so simple that we can shut them off just because we know it’s in our heads. Reality is what our brains tell us it is, a personal reality. There is a boundary between each reality making understanding ones problem unknowable unless you breach it. Yes my anxiety is all in my head, but that is my reality, it is real to me and can’t be switched off like a light.