Absolutely Fonty,
but the most experienced and most numerous fasting authorities, just happened to be Natural Hygienic practitioners.
The knowledge we have, was handed down to us from these pioneers dating from the early 1800's: Sylvester Graham, Felix Oswald MD, Robert Walter MD, Isaac Jennings MD, Russell Thacker Trall MD, Thomas Low Nichols MD, James C Jackson MD, Charles Page MD, and so on, all of whom had abandoned the drugging practice of their day by pioneering health reform, and of whom, most had extensive experience with fasting and its benefits.
The knowledge they accrued was painstakingly collected and saved into one magnificent volume by Herbert Shelton: Human Life: Its Philosophy and Laws, who then went on to write his own voluminous Hygienic System of seven volumes, which included the work of the pioneers and also included his own extensive experience as well.
I did not dogmatically say that rest was the only option. If you had read my post more carefully you would have noticed that I said that there is flexibility and room for experimentation for fasters, but this has to be seen in the context of "Fasting in Health", compared to "Fasting in Disease", the former of which is much more flexible than the latter.
All of the fasting authorities in the past agreed unanimously that absolute rest was essential to obtain the maximum benefit to recover health from any diseased state: and all Natural Hygienic Practitioners of today would say the very same thing. Do we know better than they? Hardly.
Boredom is a very small price to pay for the recovery from serious disease, which includes my own Cancer, and I very much doubt that I would be alive today without the absolute rest that I needed, and that my body craved for. Absolute rest means the conservation of all of the life's energies, to enable the body to muster all of its reserves & resources in fighting disease.
No one is banning things out of hand, like a hot bath or sauna, but with serious disease, this would inhibit the healing and cleansing process, because it is enervating to any individual trying to recover from a life threatening illness; this was proven to be so, and was the consensus of opinion by all of the fasting pioneers who denounced such practices through their own extensive experiences.
Animals also know instinctively, that to take absolute rest when ill achieves the greatest chance of survival and recovery from disease and/or injury, which is the main reason for their inactivity while fasting. Exercise/activity consumes vital resources, which need to be conserved, and is seen as superfluous by them.
There is no doubting the actual biological needs of our bodies. But you are right Fonty, good health is only achieved by taking that responsibility on our own shoulders, and to not place it into the hands of others; but we should still listen to the vast experience of those who have gone before us, who have indeed laid down rules, formulated because of their own unanimous experiences with fasting as a health achievement par excellence.
Chris