One year ago, when I was given high doses of B12 & folic acid, I developed heart failure symptoms – chest pains, shortness of breath, palpitations at the slightest exertion, and arrhythmia. I ended up in the ER. Also I was so weak that I could barely stand without leaning on something; my arms and head felt like blood couldn't pump into them -- especially if I tried to raise my arms. The same symptoms recurred a few months later when I was given B12 injections (along with IV glutathione). Reading this forum, I understand that this was probably hypokalemia – every time I was given extra B12 & folic acid, it over-drove my methylation. This must have caused a bad shortage of potassium. Around the time of those bad symptoms, my blood tests showed my potassium as 4.3. But I understand that the serum result doesn't show what is in the cells. The confusing part is, my NutrEval results (from mid-August) show that my potassium is on the HIGH side; this is Red Blood Cell potassium. The range is 2,220 - 3,626 and my result is 3,551. I wasn't having the cardiac symptoms when I had the NutrEval test, so it doesn't show what the value would be at the time of symptoms. So now I'm confused and afraid to supplement with potassium... I understand that the symptoms of both hypo- and hyper- are similar, but how come my potassium is HIGH? I haven't been eating any high-potassium foods. The cardiac symptoms always happen when I over-drive my methylation, so it should match the “hypo” scenario. The NutrEval test was done after stopping all supplements for 10 days, so my potassium level could have come up during that time, without methylation support. But still, would it go up to the high end of normal? Is the RBC potassium (as in NutrEval) a reliable marker of potassium in the cells? Any reason why over-methylation would cause high potassium, instead of low? And finally, could the cardiac symptoms be caused by a different side effect of over-methylation, e.g. high sulfur issues? (I am hetero for CBS C699T, but I never have symptoms from eating high-sulfur vegetables. But when I'm experiencing these symptoms, eating meat makes them worse). Thanks for any insights!