You may want to ask Andreas about your specific health.
I'm not familar with the intake restrictions of CFIDS / M.E/CFS, but I do know that Epsom Salts
are Magnesium Sulfate, USP (MgSO4 * 7H2O). From what I've read, Magnesium Sulfate is not recommended as a DAILY supplement to support low magnesium levels due to it's laxative properties and the increased sulfate levels, but I haven't seen any restrictions against it for ME/CFS, especially for occasional use (such as flushing or as a laxative.)
Also, when flushing you do the Epsom Salts
first so the bile ducts are relaxed and expandable. When the stomach signals for bile, the bile can push the 'stuck stone' out of the way more easily. What's happening now is the ducts are not relaxed enough to allow the 'stone' (or 'stones') through, thus creating a dam effect. Flushing may be the quickest way past your pain.
Do some more research online about ME/CFS and Epsom Salts
or magnesium. In the meantime, Ask Andreas. Tell him a brief health history and your fears then ask your questions. Either he or another forum member may be able to give you more in depth answers.