It has never occurred to most people that something they do everyday, every night - continuously - can be a source of powerful stress relief.
I remember when my father's friend was doing an awards presentation. For entertainment he said he was going to test how observant we were. He then told us NOT to look at our wrist watches and asked questions about the color, the type of watch is was, were the numbers Roman Numerals or regular English numbers and so on. NO ONE was able to answer all the questions.
Another, better known, story is about Christopher Columbus. When Columbus arrived in the new world and landed on his rowboat... the natives could not see his ship out at sea! Their familiarity with their environment and the ocean in particular was such that they couldn't perceive the ship. An elder medicine man who had the flexibility of perception had to describe the ship to his fellow tribesmen before they could see it.
This same familiarity applies to how we perceive our breathing.
Our breathing is something that we have become so familiar with that we are almost completely unaware of its effects. Consider this, our breath bridges our conscious and unconscious i.e. unconsciously we are always breathing and at any time we can consciously focus on our breathing.
This is important to remember because all our emotional states are reflected in our breathing. If we are stressed our breathing tends to be shallow and focused in our upper lungs.
In fact jerky breathing itself will actually increase anxiety and stress. While when we are relaxed we tend to breathe fully into our belly. Practicing belly breathing (diaphragmatic breathing) can be extremely beneficial.
Simply knowing this can make a big difference like remembering to breath deeply if you are stressed to feel better. In other words, you had an unconscious shallow/jerky breathing pattern when you were stressed and by consciously taking control you can choose a breathing pattern that is better for your mind and body. (which would be diaphragmatic breathing)
In Yoga, breathing is considered to be so important that before any task a yogi first prepares his/her breathing. Proper breath control is considered the key to healthy living. In fact, learning to do proper diaphragmatic breathing has been shown to reduce stress and anxiety permanently.
Diaphragmatic Breathing Sit or stand with your back straight, put your hand on your belly and breath in a slow and deep pattern. Don't try to overfill the lungs or empty them - just breath softly - expanding your belly on the inhale and contracting on the exhale. Keep your attention focused on your breathing. You will find that your mind will tend to drift. That is normal. Simply return your attention to your breath when you notice you got distracted. Allow the relaxation from this breathing pattern to spread through your body and just enjoy yourself.
Practicing diaphragmatic breathing on a regular basis will alleviate stress and give you the ability to manage your stress better. All because of some deep and slow breathing.