I can't speak for the veracity of any cures. But I can speak for the ability of state of mind to affect wellbeing.
Many years ago, during the break up of my first marriage, I suddenly doubled up with excruciating pain while walking down the street. This passed after a short while but of course returned. A visit to the GP returned a diagnosis of a stomache ulcer and referral to hospital for tests. Afew weeks later, the symptoms continuing, I arrived at the hospital, the consultant poked around, discovered my ulcer, told me it was massive, had a few students poke at it, all commenting on the size, and gave me a barium meal and an Xray. There was nothing there. The symptoms cleared up as I got over the stress of my break up.
But over a period of amonth myself, my Gp the consultant and his students were all convinced that I was gravely ill. No doubt a faith healer would have cured me quite easily.