Breathing is managed by the Autonomic Nervous System (ANS), which means you don’t have to think about it.
Now, what makes breathing unusual and different to a lot of other functions that are controlled by the ANS, is that we can also control it. Ancient yogis found this really fascinating and developed lots of different breathing patterns (pranayamas) to create different effects in the body.
When you’re stressed out, your breathing rate increases. Do you notice this? Your palms also get sweaty, your heart rate speeds up, cortisol and adrenaline flood your system and your body starts to move towards a state of Fight, Flight or Freeze.
Your body and your mind are intimately connected, by the breath. So, when you get stressed, you can use the breath to help pacify the physical responses to stress that are harder to control, which, in turn will calm the mind. The best way to do this is to activate the Parasympathetic Nervous System, AKA the Rest & Digest system, by doing long slow exhales.