Question

Why we yawn when we are sleepy or drowsy

Answer 1

When we are sleepy or feel drowsy, we yawn because our brain cells lack sufficient amount of oxygen. So, we yawn to gather a large amount of oxygen for brain cells to function properly.

Our body induce yawning to drawn in more oxygen or remove a build-up of carbon dioxide. Our brain needs oxygen to function properly and when it does not get sufficient oxygen ( a condition when we feel drowsy or sleepy), we yawn to gather a large amount of oxygen for our brain, to help it function faster and control drowsiness.