why do we yawn when we are sleepy
Kindly refer to the following link:
https://www.meritnation.com/ask-answer/question/why-do-we-yawn/why-do-we-fall-ill/1144946
https://www.meritnation.com/ask-answer/question/why-do-we-yawn/why-do-we-fall-ill/1144946