The autonomic nervous system influences and controls our basic vital functions, including breathing, heart rate, and blood pressure. The sympathetic (fight or flight) aspects of this system must be balanced with the parasympathetic (rest and digest) aspects for optimal health. A simple way to reset the autonomic nervous system, to restore neutral, is to focus on the breath:
Pause. Do 5 sequential breaths, taking 5 seconds to breathe deeply in (1-1000, 2-1000, 3-1000, etc), and 5 seconds to breathe out.
Notice that you will be calmer, and more present. You will be able to make better choices in what you do or say. This is something you can do anytime, anywhere.