Breathing

Seth Porges:

• Autonomic Nervous System: the part of our nervous system that runs automatically (without us consciously thinking about it), regulating such functions as heart rate, breathing, digestion, and sexual arousal. 
• When we face danger, part of our autonomic nervous system -- our sympathetic nervous system ("fight-or-flight" system) -- is activated, causing noticeable physiological responses. 
• Slow, deep breathing is a way to redirect or take control of the autonomic nervous system. (Most parts of our autonomic system -- e.g., digestion -- are outside our control.) Slow, deep breathing "effectively hacks into your nervous system, and causes the whole thing to change its state to one of calm." (To be more granular, slow, deep breathing activates the vagus nerve, which in turn causes "your entire autonomic nervous system to basically chill out.) 
• Patricia Gerbarg, Ph.D., author of The Healing Power of Breath, recommends "bringing things down to between four and a half and six full breaths per minute, with equal-length inhalations and exhalations. This method, which is known as Coherent Breathing, has been linked to an increase in cognitive performance and a decrease in stress."