[Oxygen is so common that it accounts for 21% of the atmosphere, but even a little shortage affects life. Oxygen is getting scarce in the room due to environmental pollution and changes in living environment.
If you live in an oxygen-free room for a long time, the amount of moglobin in the body's blood decreases, causing headaches, poor eating, shortness of breath, and vomiting.
It is also due to lack of oxygen that the head gets heavy when I stay in the air-conditioned office or in the car for a long time.] Hideki Noguchi, Ph.D.