I’ve read similar success stories from people following John Sarno, a quack who tried to put a profitable twist on obsolete Freudian junk theory. A psychosomatic illness isn’t “all in your head”; it’s a physical condition caused or spurred on by psychological factors. Stress is a great way to set yourself up for a host of illnesses, including chronic infections. It’s not inconceivable that something that helps to alleviate a significant chronic stressor could produce pretty miraculous health improvements, especially coupled with the placebo effect. I’d say stress reduction is a major part of the placebo effect.