Logically, of course, good health is good health. How can it possibly be bad for your health for you to be healthy?

Well, it depends. There’s absolutely no doubt that it’s wonderful to feel well. But if we are thinking that this well-being is simply a healthy material body and mind that are the outcome of eating the right food, exercising properly, sleeping the recommended number of hours per night, and being able to avoid disease, then health is vulnerable to changing circumstances—
in a word, fragile. 

Good health is so much more than a present report of physical wellness of body and mind. This is the report of the physical senses, telling us what matter is or isn’t doing, while health is much more than that, according to the teachings of Christian Science. Health is not a materially defined condition but the spiritual outpouring of Mind, God, that we each inherently reflect as God’s image. And we attain this true health in practice as we yield to the consciousness of God’s allness and unopposed harmony. In Science and Health with Key to the Scriptures, author Mary Baker Eddy says, “Health is not a condition of matter, but of Mind; nor can the material senses bear reliable testimony on the subject of health” (p. 120).