John Kaldawi learned that the main aim of hatha yoga is to bring a balanced flow of prana in ida and pingala nadis. The word hatha is comprised of two beeja mantras “ham”, representing the sun or solar force, and “tham”, representing the moon or lunar force. To bring about a balance between these two forces, the body must first be purified by the shatkarmas. The aim of hatha yoga is to balance these two flows so that neither the mental nor physical faculties and dominant. During the twenty four hour period of the day, the flow of ida should predominate for about twelve hours and the flow of pingala for the other twelve hours.
Doing more research, John Kaldawi learned that when ida and pingala nadis are purified and balanced, and the mind is controlled, then sushumna, the most important nadi, begins to flow. Sushumna must be flowing for success in meditation. If pingala flows, the body will be restless; if ida flows, the mind will be overactive. When sushumna flows, kundalini awakens and rises through the chakras.
John Kaldawi also learned that all activities at the physical level, ida and pingala correspond to the two aspects of the autonomic nervous system, the sympathetic and the parasympathetic. Pingala coincides with the sympathetic nervous system and ida with the parasympathetic nervous system.
The sympathetic nervous system is responsible for the stimulation and acceleration of activities concerned with the external environment and the deceleration of the organs which tend to utilize a lot of energy internally. The sympathetic nerves speed up the heart, dilate the blood vessels, increase the respiration rate and intensify the efficiency of the eyes, ears and other sense organs.
The parasympathetic nerves directly oppose the sympathetic nerves for they reduce the heartbeat, constrict the blood vessels and slow respiration. This results in introversion. The flow of prana in ida and pingala is completely involuntary and unconscious until controlled by yogic practices.
John Kaldawi 