Question

Why do we yawn when we are sleepy? what is the biological processes that takes place?​

Answer 1

This is a myth that when we are sleepy then only we yawn but actually the reason behind this is----

Our body takes less oxygen when our breathing is slowed therefore yawning helps us to bring more oxygen in our blood and move more carbon dioxide out of the blood .

hope this will help you

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Answer 2

We yawn when there is a reduction in the level of oxygen in our brain. By yawning we take in greater amount of oxygen which accounts for the oxygen drop