Oxygen content is not directly related to what we usually call fatigue, is it? I'm not sure. I didn't listen well in class )

The main reason for dozing off is that central nervous system fatigue is normal. My body recruits a large number of muscle fibers under the condition of rapid repetition and high load, and the level of acetylcholine drops to a certain extent, causing fatigue of the central nervous system. I'm usually so sleepy that I can't even drive after practicing my legs. I have to sleep in the car for 20 minutes before I can go home.