Breathing is a vital element of hatha yoga. Practicing yoga breathing or breath control in yogic terms is called pranayama. The word Pranayama can be broken into two parts: Prana means life force and Yama means control. By conscious control of the breath, you can create a proper rhythm of slow, deep breathing. Prana is not the air itself but the subtle life-giving element extracted from the air. The more life-force you have in your body, the more “alive” you are; the less life-force, the less “life”.
Alternate nostril breathing is a breath purification technique in Hatha yoga. It balances serotonin, the brain chemical that regulates and contributes to equilibrium between the left and right hemispheres of the brain. Yogis believe that this exercise will clean and rejuvenate your vital channels of energy, thus the name nadi sodhana (purification of nadis or channels).
At any time one nasal passage is dominant and functioning. One nostril is much easier to breathe through than the other at any particular time and that this alternates about every three hours. Scientists also discovered that the nasal cycle corresponds with brain function. The electrical activity of the brain was found to be greater on the side opposite the less congested nostril. The right side of the brain controls creative activity, while the left side controls logical verbal activity.
All set and done, but if you cannot breathe due to mechanical blockage like a deviated septum, polyps,rhintis, what you do? No body seems to give an answer.My advice is to go to an ENT doctor, get your nasal problems sorted out then start Yoga.