Yogis tell us that moon is the presiding deity of Ida and sun is the presiding Deity of Pingala. That is why sometimes the left nostril is flowing, sometimes the right and sometimes both. When left flows, it is the Ida nadi that is operating. At that time one should perform simple and peaceful works. But when the right nostril is flowing, it is Pingala that operates. Then one should do vigorous and hard works such as exercises, eating, bathing, etc. Also , one should sleep during that state , because Pingala digests the food quickly and bestows sound sleep.
But when both the nostrils flow, it is Sushumna nadi that is operating. That is the time for the practice of meditation, repetition of the Lord’s name, prayer and enquiry.
Sushu8mna, the best of all nadis, arises from the basal plexus and passes through the spinal column, through the subtle channel of the spinal cord, up to the crown of the head. All Chakras or mystic centres are situated in it.