I watched a video a short while ago that was posted on Parley. I can't find it now, but the woman who made it, told people to go out and buy one of those oxygen meters that clips on your finger, if you want to check your oxygen levels. She had a graphic that showed oxygen levels, and what the danger zones are. She cited the story of two boys in China who recently died after participating in gym activities while wearing masks:
Two boys drop dead in China while wearing masks during gym class
Thanks, I may need to get one of Those oxygen gauges. I could not believe how suddenly I was gasping for breath And pain in chest , when carrying books upstairs with a face mask on. Now I NEVER wear one if I’m doing anything slightly strenuous.