This mysterious experience seems also to have been known to Dionysius the Areopagite. It is definitely an experience terminating the process of meditation, for the mystic can then go no higher and no deeper. It is variously called "the Nought" in the West and nirvikalpa samadhi in the East. Everything in the world vanishes and along with the world goes the personal ego; nothing indeed is left except Consciousness-in-Itself. If anything can burrow under the foundations of the ego and unsettle its present and future stability, it is this awesome event. But, because it is still an experience, it has a coming and a going. Although it is forever after remembered, a memory is not the final settled condition open to man--for that, philosophy must be brought in. Mysticism may remove the ego temporarily after first lulling it, but philosophy understands the ego, puts it in its place, its subservient place, so that the man remains always undeserted by the pure consciousness.
-- Notebooks Category 20: What Is Philosophy? > Chapter 4: Its Realization Beyond Ecstasy > # 116