"The yogic concept of prana is widely known and accepted today, but thirty years ago it was virtually unheard of. At the Minninger Foundatino, Swamiji explained prana by saying that it is the subtle energy – the life-force- that holds the body and mind together, adding that if we want to lead a healthy life, it is important to keep this energy in a balanced state. Breathing is the most obvious manifestation of this subtle energy. Normally when we breath, one nostril is more open than the other, and so we supply more air to our lungs through that nostril.
[…] When the balance between the flow of the right and the left nostril is upset, the pranic energy is affected by it, and the result is some sort of physical ailment, sometimes trivial, and sometimes more serious. If we want to cure ourselves of disease and restore the balance of life, we should try to restore the balance between the flow of breath. The breath flow should therefore be carefully studied for the purpose of getting rid of diseases. Not only does breathing oxygenize the blood but it also stores up pranic energy. The breathing not only coordinates the positive nad negative currents of the body but also attracts desirable and undesirable conditions. […] This pranic energy, if it is wasted, causes diseases"
Extracted from "At the Eleven Hour" by Pandit Rajmani Tigunait, Ph.D