Been there, when the smoke alarm goes off (actually happened last year), you know it is too much. Or when I am reaching for my inhaler (asthma), time for some fresh air.
My wife had a coughing fit and bruised her stomache muscle wall in so much pain had to go to ER. We had no idea what was going on so we feel blessed to be out of there and home. Kids did not even know we were gone.