Masks also upset the normal oxygen/carbon dioxide ratio, which is a very delicate system in the body. On two occasions, both at medical facilities that required masks, my normal BP skyrocketed when my ratio was thrown off by breathing too much carbon dioxide. In both cases, medical personnel were alarmed, and I felt myself getting into trouble fast. I have medical documentation to prove that my CO2 went out of normal range, and chart info that should show the beginning of a medical crisis in both cases. I also have previous documentation of these test results without a mask (CO2 within normal range and no resulting BP spike).