The Placebo Effect

Are you ill simply because you believe you are? That could very well be the case, as studies involving placebos have shown.

A placebo is a forged medicine, given to a patient without them being aware of it being a sham. Instead, the patient believes it to treat whichever illness he or she suffers from. They do not know, and are usually never told, that the pill or other form of medicine they are taking is not what they were told was prescribed. With the patient believing the "medicine" they take to be effective, they gain hope and confidence in a recovery. This willpower can then become a treatment for the illness - a treatment dubbed the Placebo Effect.

http://en.wikipedia.org/wiki/Placebo

http://www.scientificamerican.com/article.cfm?id=placebo-effect-a-cure-in-the-mind