Dr Robert Svoboda (whom I highly recommend) points out that people with multiple personalities can be allergic to something if they eat it when one personality is present, and not when another personality is present. This effect of the personality extends to the physical realm in such things as being right or left handed, wether the eyes squint and even the curvature of the lens.
Ther are many cases reported where if one personality is drunk, when another personality enters the body they are instantly and totally sober. Different personalities react differently to drugs and medication, and, in the case of women, can even menstruate many times in a month depending on which personality is present.
So what's this got to do with anything? It simply demonstrates the physical effect of the things that are not physical.
Unfortunately since we are not fully conscious of these things we can't fully control them. But being aware that your personality (however many of them there are!) has such a big impact on your physical body can be very useful in Ayurveda. Fear, for example, causes diarrhea, and even fear of diarrhea can cause diarrhea itself. So if we can detach ourselves a little from our fear perhaps we can become a little healthier and stronger.
I believe meditation is the key to becoming more aware of the personality and ego, our attachments, desires, karma and our emotions. Emotions are, afterall, just chemical reactions in the brain. And the brain wave patterns are triggered (as demonstrated by people with multiple personalities) by our personalities. A little awareness of this human condition of being controlled by our personality can actually improve our health.
I'm not suggesting we can all cure ourselves, because that would imply that it's your fault if you are sick, but it certainly won't do any harm to practice a little detachment.
Just what I've been thinking about. I'd love to hear your thoughts on the matter.