I'm writing using my wife's account since she is too ill to write herself. She has had ME/CFS for a number of years, increaslingly getting worse. When she last visited her doctor she was prescribed B12 injections (hydroxocobalamin). Since she is very sensitive to side effects she started with a tenth of the prescribed dose (which was 1 mg - she started with 0.1 mg). 20-30 minutes afterwards she started to feel an increased fatigue and kind of a pressure across the chest. She felt it got harder to breath normally.This is 10 days ago. Since then she has felt that these symptoms have gotten worse. It seems unlikley, but could this really be caused by that single injection? And if so, do you have any insights as to why this happened?