Question

Paheli wants to know why we yawn when we are sleepy or drowsy.​

Answer 1

Answer:

One is that when we are bored or tired, we just don't breathe as deeply as we usually do. As this theory goes, our bodies take in less oxygen because our breathing has slowed. Therefore, yawning helps us bring more oxygen into the blood and move more carbon dioxide out of the blood.

Explanation:

Answer 2

It is so because our brain needs to take oxygen and by yawning our mouth increases its size and takes many of oxygen from air fir brain.

You can tell this answer to Paheli.