So how does it work?
Your autonomic nervous system, which controls involuntary actions like heart rate and digestion, is split into two parts. One part, the sympathetic nervous system, controls your fight-or-flight response. The other part, the parasympathetic nervous system, controls your rest and relax response (RightAsRain).
These two parts of your nervous system cannot be activated at the same time, which means if you work to activate one, the other will be suppressed. In other words, breathing techniques will trigger relaxation, which prevents you from experiencing the potential panic of a fight or flight response.
Breathing more deeply also allows for more carbon dioxide to enter your blood, which quiets down parts of the brain, such as the amygdala, a structure implicated in the anxiety response. More carbon dioxide also helps synchronize your heartbeat and breathing, balancing the brain/heart’s electric signalling. This process is called heart rate variability, and it is known to be important in determining our moment to moment experience in stressful situations.