While fasting and using a suana may be a bad mix, fonty is right when he states that there is room for experiementation. Fasting as we know is not an area that has been extensivly studied in contemporary culture.
Maybe for the very ill that are fasting, resting is the only option because they need to maintain their lifeforce. But for those who aren't truly ill that are fasting for a better life there are more options open to them.