Breath

Yogis have said that almost all illnesses can be resolved with breathing. From my personal experience, I have found this to be true over the years, though I have no proof.
Nevertheless, regardless of lack of proof, I do know that without breath, there is no life. Breathing ranks up there in the hierarchy of needs. Most people can go without food for eight weeks, without water for four weeks, but lack of oxygen is much shorter--seven minutes. It is a premium. That seven minutes is all most people get, and even before that portions of the brain would become damaged.
Interesting facts, but how does it factor into overall health and well-being?
Easy.
When under stress, acute or chronic pain, or lack of training, many people breathe shallowly, creating inefficient oxygen supply and delivery to all areas of the body. If prolonged over time, even just a few months, lack of proper oxygenation can lead to deterioration of your health. It can cause health problems, such as headaches, stiffness, and lethargy.
When combined with pain or stress lack of proper breathing can impede your body's ability to get better, in other words: heal thy self.
What does inefficient breathing feel like?
Typically, you are only inhaling air shallowly into your lungs, thus chest-breathing. There might be a feeling of shortness of breath or not being able to "catch" your breath.

How do you correct this?
Diaphragmatic Breathing: Lie on your back (floor or bed) with your knees bent and rest a book (1-2 pounds) or your hands over your navel. Then, as you inhale (slowly) try to fill your belly, thus pushing the book or your hands up. Upon exhale let your belly fall towards your spine. Do this gently without forcing and this will naturally deepen your breathing and better supply oxygen to your system.
Enjoy!!
References:
Ramacharaka. Science of Breath.