We breathe through one nostril at any given point of time. Every hour & twenty minutes the dominant nostril switches over.
When the left nostril flows, mental energy dominates
When the right nostril flows, physical energy dominates
When both nostrils operate together, mental & physical energy patterns become even & rhythmic, the thoughts are stilled & the mind is calm
This is Shoonya Swar – Time to meditate
– Shivaswarodaya Shastra