IIRC, this is because the aveoli in the lungs can still expel the CO2, but have a tough time with oxygen intake. It is CO2 build up that makes you feel distress

IIRC, this is because the aveoli in the lungs can still expel the CO2, but have a tough time with oxygen intake. It is CO2 build up that makes you feel distressed, not necessarily the lack of oxygen.