I've been thinking a lot lately about hypophosphatemia. It is the hallmark of refeeding syndrome (in addition to hypokalemia and hypomagnesium), and can cause profound muscular weakness. Based on symptoms caused by a couple of different supplements, and resolution thereof with high-phosphate foods and monosodium phosphate (initial boost in energy followed by severe weakness with B1, B12, and possibly arginine) I think hypophosphatemia may be quite common in people with ME/CFS, only it is rarely diagnosed. Also see: http://www.ncbi.nlm.nih.gov/pubmed/9683977 Foods high in phosphorus include yogurt, kefir and sunflower seeds, all of which have helped me. I can now take B1 without that horrible weakness and was able to increase my B12 as well, which I could not otherwise do. Also, Swanson Vitamins has a product called monosodium phosphate which I've taken in quite small doses as well when needed. So here's a wiki article on it: https://en.wikipedia.org/wiki/Hypophosphatemia#Major_signs_and_symptoms @Gingergrrl - I was thinking of you and your breathing difficulties and wondered if anyone had checked your phosphate levels.