Why we yawn ielts reading?

Question: Why we yawn ielts reading?

As soon as we sit down to study, it is natural to yawn and this is a very interesting question. Because as soon as we sit to study, we yawn, then people have this concept behind it that at that time we feel like sleep and the amount of oxygen in our body decreases due to this, but it is believed by scientists. That's why it comes. Because our brain needs to cool down and it cools the brain and makes it for more use. But people believe that it comes due to fatigue.