Actually, a lot of the Old Age traditions and beliefs have diseases and illnesses as coming from spirits, and some of the people who follow those traditions and beliefs today can and do treat diseases and illnesses in this way. It's not always necessarily so that it literally removes all traces of illness, more so that it allows one to better heal.
I've worked with spirits of illness and disease in order to curse a person before, and they were more than willing to help me out in making another person ill (I even took some of these outside of my own body).
I've also read some incredible stories of how positive thinking and positive energy has allowed people to overcome illnesses and diseases that otherwise kill many. It's all dependent on the disease/illness and how it can be fought. Never assume that metaphysical healing will 100% cure you, always be willing to do other treatments in order to assist with your condition. Even in ancient times, medicine and magic were mixed together in order to give the patient the best results possible.