About 15 - 18 years ago I got some nasty Flu. Blood o2 got down to about 56% and was getting tunnel vision.
Went to the Hospital & they freaked, cause when that happens the heart likes to protest by quitting.
Nine others in there with the same Flu at the time.
Couldn't breath. Spent 3 days in there & ended up with lung damage from it.
Only time it slows me down now is when there is lots of smoke.
Dusty conditions like a few days ago - high winds & dry conditions + farmers had just planted their fields. Dust was like fog , at times couldn't see 20 yards.
Or when I mig weld too much
Four different drugs to inhale keep me going.