eli5:Why do we yawn?

Question

Basically the title. Why do we yawn when we are tired?

In: 2

Answer 1

Generally, yawning is a sign that your blood oxygen level is getting low so you take a sharp deep in breath.

There can be many reasons to trigger a yawn, usually tiredness. The brain slows down and your temperature drops and your breathing rate. But your not actually asleep so you need a steady blood oxygen level so your brain panics and makes you gasp for air.

You can also yawn when exposed suddenly to bright light, boredom, anxiety, stress, a side effect from anaesthetic and sometimes as a vasovagal reaction when your having a heart attack.