Prolonged diarrhea is dangerous...no matter what the cause! Make sure that you rehydrate yourself with lots of water and replace lost electrolytes.
The Epsom Salts serve two functions. The magnesium contained in it helps to relax muscle tissue, including the ducts so that 'stones' can be expelled more easily. It also works as a digestive flush (NOT the same as a colon cleanse!) so that you rapidly expel any released toxins and 'stones'. Taking a high dose of magnesium would serve the former purpose without the laxative effect. A lower dosage of Epsom Salts or an herbal laxative tea would take care of the latter.
It is not necessary to use something with such a strong laxative effect (for you) in order to receive the benefits of the cleanse.