In mental terms,
(2) The rhythm is the action of the mind, whether the mind is active in harmonious thoughts or in inharmonious thoughts, whether the mind is strong, firm, and steady, or whether it is weak. If one continues to think harmonious thoughts it is just like regular beating of the pulse and proper circulation of the blood; if the harmony of thought is broken, then the mind becomes congested. Then a person loses memory; depression comes as the result, and what one sees is nothing but darkness. Doubt, suspicion, distrust, and all manner of distress and despair come when the mind is congested in this way.
(1) The Prana of the mind is maintained when the mind can be steady in thoughts of harmony; then the mind can balance its thoughts, then it cannot be easily shaken, then doubt and confusion cannot easily overpower it.