During the fast, the body will redirect its energy towards healing and fighting what made you sick in the first place, mostly pathogens. Those live essentially in the intestines. When they die, parasites and candida release much more toxins than alive. Enemas remove those dead pathogens and their toxins quicker so the elimination organs such as the kidneys and the liver are not overburdened. That's why everybody feels better after an enema.
Not using enemas during a healing crisis is just STUPID, sorry to say. It can even have fatal consequences in very sick people. Dr Gerson understood this well when his sick people would die of liver failure on his protocol. Only when he introduced the use of enemas did he see them get better FAST.