Most are mental or have a mental component. Of all the Psych. To get this to happen, he sounded a bell before feeding the dogs at many sequential feedings. At any rate, that and other emotional or automatic responses originate in the so-called subconscious mind. You normally cannot control it by your will, but you can influence it using your imagination.
Headaches are only one common example.
People spend thousands of dollars for medicine and doctors and suffer needlessly with conditions that are purely psychological. These normally considered physical conditions are mostly curable or brought under control with only a few moments of competently administered suggestion, and I don't mean in a trance. A sugar pill, bad-tasting medicine or a hypodermic of sterile water is a very potent suggestion when properly administered. I learned the tremendous power of a properly administered suggestion from native healers in the Philippines, mostly scoundrels. But they were often effective beyond belief.