Our lungs are composed of little tiny sacks for absorbing oxygen called alveoli. When you’re breathing normally, the small air sacs in your lungs can sometimes collapse spontaneously. This can negatively affect lung function and reduce the gas exchange that occurs there.

These involuntary deep breaths or sighs help to prevent the alveoli from collapsing because it’s such a big breath, it serves to reinflate most of your alveoli.

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Is there a reason I took a deep breath while reading this?

Awareness e.g. You start thinking about it.

For example, after reading this sentence, you might find an itch on your nose

Yes, you are slowly dying. With each breath you are closer to death. Have a nice day.

Interesting, so I wonder if it’s like a pre-fight or flight deal. Your body anticipates a need for rapid breathing so it is planning ahead.

I think it's natural selection. We evolved with alveoli as the gas exchange mechanism in our lungs. If you didnt have the genetic code for this automatic response, you didnt have as many offspring.

Or become aware of the size and position of your tongue.

Now try to forget it.

Great. Now I'm itchy, I yawned, I took a deep breath and I'm fucking stuck on Manual Breathing now.

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I’ve seen baseball pitchers often take a deep breath before they pitch. It’s clear that their deep breath is relieving pressure or tension. It seems to function similarly in OP’s “out of nowhere” state. For me, it seems to relieve stress… like a deep sigh. Something of a ‘relaxation reset’.

fuck this comment in particular

Yeah I get that, but isn't that a deliberate choice to get your body in certain state before making a quick and precise motion (like snipers timing their shots with their breathing)?

There's no way you saw me