Why people yawn when they are sleepy? Are there any biological reasons behind yawning?

Question

Why people yawn when they are sleepy? Are there any biological reasons behind yawning?

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Answer 1

When you sleep your body does not require as much oxygen as it would when you are awake and active so your respiratory system slows down. One theory is that when we get tired our bodies begin to pivot to this period of low resource usage but if we are still awake will cause us to yawn as a means to get an influx of oxygen that we need.

Edit: I realized that it’s an old theory… more reading led me to the idea that it’s the body trying to stay awake not as much reacting to trying to be awake.