Thanks for bringing forward the NH view on vitamin supplements although, to be truthful, there are plenty of Hygienists who have lost faith in the Hygienic principles and are recommending some supplementation. Bernarr Zovluk's take on this is that those with limited faith are just unaware of how to properly practice NH. In the end, it's down to the individual to decide who they will trust.
I can assure Smashbtws that their weakness is not down to vitamin or mineral deficiencies. It will be completely down to the detoxification process and will pass as the bloodstream purifies.
Any attempt to relieve the symptoms of this process will only work by interrupting the process and is a bad idea on several levels. What is the point of fasting if you're going to interfere with it thereby wasting the energy resources being consumed. You'd be better off just eating healthily and detoxing in slow time.