I know that wearing a mask is uncomfortable, tiring, and might leave some feeling exerted or lightheaded. I’ve never denied that and can understand that from personal experience. However, it isn’t true that the reason is that they block oxygen. I appreciate that you are open minded to challenge what you believed. That seems more and more rare these days but increasingly valuable.
I find my breathing pattern changes with a mask as I tend to exhale more deeply to push warm air away. Breathing deeply or with more exertion can cause lightheadedness. Part of the reason is that deeply exhaling removes more carbon dioxide from your system which can result in dilation of blood vessels in extremities and a decrease in blood pH. A lower blood pH also causes hemoglobin to bind oxygen more tightly thus making it harder for cells to exchange. Both might make it seem like you are oxygen deprived but it isn’t because you are breathing in less oxygen. In fact, the theory behind breathing in a paper bag when hyperventilating is to rebreathe exhaled air with carbon dioxide to restore normal carbon dioxide levels. Exercise or heavy exertion will lead to deeper exhaling so you’d probably feel lightheaded wearing a mask in those conditions.
I sympathize with anyone wearing them for long periods.
