There's an old Japanese Proverb - "Yamai wa ki kara", which means "sickness is a thing of the spirit." I'm not an expert on things oriental, but that appears to be an accepted piece of folk wisdom in Japan, along the line of "many hands make light work" or "a stitch in time saves nine" here in the West.
That bit of wisdom has been independently incorporated into the Creed of the Church of Scientology in these lines: "And we of the Church believe that the spirit can be saved and that the spirit alone may save or heal the body."
Having been sick myself plenty of times over the years (mainly with the flu and various other bugs), I find that Scientology assist (particularly a touch assist or nerve asssit) helps me greatly in getting over them quickly and regaining my footing in life. These assists help my body heal up faster. It's not so much "mind over matter" -- which, by the way isn't a datum that came from Scientology, we would phrase that more along the line of a "spirit being cause over matter" -- as it is similar to the chiropractic principle that a body "knows" how to heal itself and will heal itself if it allowed to to so. What prevents it from regaining good health? Aside from bugs and viruses that can usually be singled out and killed with antibiotics or other medicines, there are thoughts, mental masses and such things, mental phenomenon, that can prevent a body from doing its job correctly. That's what I've experienced, anyway. YMMV. I've delivered many hours of assists on other people, usually short sessions that always end with a smile, an understanding of some kind. Giving others assists -- being willing to help others -- is a basic part of being a Scientologist. Help is something we are not ashamed of giving, or receiving.