"The complex has its roots in the simple."  Lau-Tzu 

The entire autonomic nervous system (and through it, our internal organs and glands) is largely driven by our breathing patterns. By changing our breathing we can influence millions of biochemical reactions in our body, producing more relaxing substances such as endorphins and fewer anxiety-producing ones like adrenaline and higher blood acidity. 

It is one thing to be alerted to a threat but altogether another to over react with a tendency towards fear, to fight, to flee, to feint, freeze, fake it, fumble, mumble or stumble or become addicted to some inappropriate action like drinking, smoking, fighting, sexing or some excessive activity.

There are two ancient laws. "Breath is life" which I am sure most of you have heard and  "control your breathing  and you control your life". Your breathing produces over 95% of your energy and drives your nervous system some place in between a blind five your old child at the wheel of a fast moving bus in rush hour traffic or a skilled race driver at the wheel of a 200 mile per hour vehicle; smooth and calm. To try to change a bad habit without changing your breathing pattern is a little or a lot like swimming upstream in against a mess of logs, boats and debris coming downstream.   

There are many causes of anxiety.  Food additives, sugar, alcohol, adrenal dysfunction, prescription or recreational drugs are some.  Situations in life that are threatening or even seem so will cause anxiety. The idea you do not have enough time is a huge cause of anxiety. Taking on too many projects or responsibilities invites anxiety and we too often forget we chose and often can un-choose some or all.  Spending too much money, getting into debt and worrying about that will cause anxiety.  Being out of work is huge. Eventually a certain level anxiety becomes an every day occurrence that we sort of get used to. The distorted breathing pattern sets in and never leaves and then starts "driving the bus".   In other words bad breathing from excessive stress or anxiety  or trauma invites more bad breathing and/or anxiety/nervousness which causes worse breathing which causes more nervousness and failed attempts to change that state of being: it feeds itself. When the breathing is not allowed to stay in balance every reaction to life becomes distorted or negatively magnified.

Generally the first line of defense if to remove a negative stimulus. The caffeine you ingested is driving you up the wall? Stop drinking caffeinated beverages.  If there is snake in the area, remove the snake or leave the area. Your environment is inviting too many temptations to act inappropriately and you feel the need for a safe house, retreat center or an island in the Pacific where you can leave it all behind.  If this is impractical, (your boss is the "snake" or he/she is just so exciting you just cannot sit still), you take side effect causing prescription drugs that make you nervous and you just need some time to calm down. You often can reduce your anxious reaction(s) by the way you are breathing.  You can consciously slow your breathing down in a balanced way and reduce the anxiety level; at will and often totally. "Control your breathing and you control your life". Breath is life.

This can be quite helpful but is often a temporary approach and your body may need more oxygen in the first place so slowing the breathing down may or  may not be a good idea albeit a momentary quick fix and sometimes even life saving.  The long term best approach is to manage the immediate anxiety and then change/develop your breathing so that it automatically adjusts and you stay calm and do not get over anxious in the first place. "Courage under fire" might be one way of looking at it but it is really more about grounding, relaxing, and feeling safe and calm inside one's self.  

In other words, one's can interpret anything something as negative and the breathing over-reacts in an unbalanced way and that makes nervousness get worse even up to full blown panic, high blood pressure, migraine, hot flash, ulcer, constipation, heart attack or stroke. It also occurs in the reverse. The breathing is now semi-permanently out of balance and invites overreaction to perfectly harmless events and what was an imagined threat now causes a reaction that can be just as damaging as a real threat. 

The way you breathe can make you sick or make you well.
When your breathing overreacts in an unbalanced way your body often tightens in several areas.  Or you hold your breath or breathe shallowly to try to stay in control which only worsens the situation by creating oxygen deprivation and more tension which heightens the stress response and then the tension sets in to stay. This further restricts respiration and produces shallow, rapid distorted breathing.  Shallow breathing numbs our feelings and traps the anxiety inside, blocking smooth energy flow, which in turn triggers more physiological or psychological arousal, sending us up the anxiety and confusion escalator and then possibly down into depression, malaise and confusion.  I see what is often called psychosomatic illness greatly stemming from this.