If aum is used only as repetition upon the mind, its impact brings hypnotic sleep, what is called yoga tandra. But if aum is pronounced with the witness well established within; if you are fully awake and are listening to the sound without drowning in it, without getting lost in it; if the sound is on one plane and you are standing on another as the listener, the observer, the witness; if you are fully awake to the sound – then only can work on the second possibility of the fourth plane begin. Then you will not go into yoga tandra, but into yoga jagriti, wakefulness.
I strive constantly to keep you away from using mantras. I always advise you not to use any mantra or any word, because the chances are ninety-nine out of a hundred that you will go into an imaginary trance. There are reasons for this. The fourth plane is vulnerable to sleep; it knows only sleep. Its dream track is already there. It dreams every day. It is just as if we were to throw water into this room. After some time the water will dry up, but it will leave a mark on the floor. Then if we throw water again on the floor, this water will flow along the same tracks as previously.
The greater possibility with chanting and mantras is that your mind with its tendency to dream will at once fall into dreaming through its own mechanical process. But if you are fully awake and witnessing inside, observing the sound of aum without merging into it, without losing yourself in it, then it could do the same work as repeating, “Who am I?” – which I advocate. Now if you ask, “Who am I?” in a sleepy state and are not a witness, the same error can take place here and you will merely be dreaming. But the possibility of this happening with “Who am I?” is less than with the repetition of aum, and there is a reason for it.
With aum there is no question asked; it is only a gentle touch. With “Who am I?” there is a question, not a mere pat. There is a question mark after “Who am I?” and this will keep you awake.
It is an interesting fact that when there is a question in the mind it is impossible to sleep. If a difficult question revolves in your mind during the day, it spoils your sleep at night also. The question will not let you sleep. The question mark is the partner of sleeplessness. If there is any question, any anxiety, any curiosity in the mind, it is difficult to sleep.
I suggest “Who am I?” in place of aum because basically it is a question, and since it is a question it is an intrinsic search for an answer. Besides, you will have to keep awake for the answer. In aum there is no question; it has no sharp corners and hence it does not strike you. It is absolutely round and there is no question. Its continuous gentle strokes generally lead only to imaginary trance.