Deep breathing is what the American Institute of Stress calls a "super stress buster."
When we're anxious and stressed, it can cause you to take shorter breaths, so by deliberately taking a series of deep ones, you can help increase the supply of oxygen to your brain.This, in turn, stimulates the parasympathetic nervous system, sometimes referred to as the "rest and digest system," because it's the part of the nervous system that slows heart rate, increases intestinal activity, and relaxes certain stomach muscles.