Sadhana means spiritual practice. It is the 10% of our time that we give to God in the ambrosial hours of the morning.
The radiance of your spirit can be measured according to how the name of God vibrates within you and around you. If your sadhana is perfect, your spirit will be high. If you have forgotten to chant the name of God, you will be in the doldrums. If you become low and depressed, it is only because you have not warmed up your machine in the morning; you have not done your spiritual practice. Your mind has found the zero point through working the belt of meditation. And if the mortal does not work the belt of meditation, then the electricity is not produced and the generator does not work. The mortal must work the mind; the mind must become zero, and it must create the experience of Infinity within you. In the Western world where there is such a criss-cross of mental thought patterns, you must find a way to bring your mind under control. You must learn to bring the level of yourself to zero, whenever you like. This is practiced in sadhana.
Remember, you are you and you are not you. You are you in the frame of the defined finite, but you are not you, in the frame of the Infinite. In your consciousness, you must find a time to think. It is very important. At this time there are 3 questions you must ask yourself: (1) "How much am I a part of the I AM which made me what I am?"; (2) "During my working day, during my existence, during my awareness, how much of the time have I been aware that I am part of the greatness that I am?"; and (3) "What can I do to extend myself to the greater I AM of which I am a part?" In finding the answers to these questions, you will find your way from the realm of finite ego to the realm of higher consciousness, and you will have the experience of total relaxation into mental happiness and contentment.
From the book Ancient Art of Self Healing which is a collection of excerpts from lectures, notes and classes by SSS Harbhajan Singh Khalsa (Yogi Bhajan)