As a general rule when folks get ill when they begin fasting it's and indication of a very congested system. Were you having at least on good unassisted poop per day before the MC?
Experienced fasters will start at least a week or 2 before a fast to prepare and get the system gradually detoxing by eating raw and drinking fesh made juices. If they are cafiends then they need to wean of that too. or if they were diet soda addicts.