I did a big project on psychosomaticism my Senior year in high school (read: 15 pages). You would be absolutely shocked at some of the things your mind can do when it is tricked to believe some things. I would have to look up the article, but the biggest example that sticks out in my mind was an incident in England a few years ago where someone made it appear that toxic gas was coming out of the vents in a grade school (the gas was really quite harmless). Two thirds of the students affected by the "gas" were takin to the hospital because of real physical problems.