Why is it easy to get sleepy when sitting as a coach?

It's easy to get sleepy by bus. On the one hand, because the space inside the car is relatively small, we will feel uncomfortable if we stay in this space all the time. And if we do it for a long time, the air quality will become very poor, because the carbon dioxide content around us is too high, which will easily lead to your lack of oxygen. Of course, you will want to sleep, want to sleep.