Are you saying that the illness is in my head?
Not at all. Stress is physiological. Think about what happens to your body when you are startled by something or if you have to give an important presentation in front of lots of people, for example. The mind and thinking component to this is of minimal influence. Our bodies have evolved over thousands of years to help us to survive. Our bodies cannot tell the difference between the threat of being chased by a lion and being subjected to ongoing abuse from a tyrannical boss or parent.
We cannot be expected to think our way out of stress. We cannot override our automatic physiological reactions with our minds. We need to work at the level of the nervous system to process the stress that has built up in our bodies over time.