In the East, non-dual teachings are referenced by the term Advaita Vedanta. In Sanskrit, "Advaita" means "not two" and "Vedanta" means "the end of knowledge."
"Not two" does not mean that there is therefore "one." It means that there are not two.
The absolute reality is beyond perception and cognition. This means that it is beyond knowing; beyond perceiving and conceiving. In other words, reality cannot be understood or learned. Further, one cannot look for it like an object in order to perceive, observe or notice it.
Being beyond perception and cognition, the ultimate reality does not perceive anything or know anything, since only It is.
It perceives and knows only through its power of consciousnes; itself being prior to consciousness.
Only Pure "I" stands alone; the absolute reality.
While my power of consciousness is dependent upon me and it cannot stand alone, my power is inseparable from me.
We are able to understand and perceive what we are not. Understanding in itself is not enough. The false must also be directly perceived. In perception, what is false falls away spontaneously on its own accord.
Traditional Advaita is the progressive exclusion of what the absolute reality is not, so that there is right understanding followed by direct perceiving. One could say that Advaita is like a road map that is useless in itself until you have actually driven the way.
Perhaps an analogy might help support this word "progressive." In the United States, if one is driving from Seattle to L.A., more likely than not, one will pass through Portland and San Francisco before arriving in L.A. This is a "more likely than not" situation. One morning, you could simply wake up in L.A. and have no idea how you got there.
In Self-realization, the idea of progression is false, yet the understanding and perceiving of the false 'burns' the altered states of consciousness into pure consciousness, so that the tendencies do not service later for eradication. However, either way all is resolved.
The important fact is that you are already that which you are seeking; this is not a new attainment and "becoming" is not the right approach. It is a postponement strategy.
Advaita is not a path or practice and does not indicate a new set of beliefs and concepts. In the absence of the false (ignorance), the Absolute stands alone and may be realized.
Enlightenment is not an experience and is beyond knowledge, since it is beyond perception and cognition. There is no experiencer and no experience. There is no perceiver or perception. The points of reference of the experiencer or the perceiver (the witness) is eliminated. It is the great disappearance of the universe.
Self-realization is realizing the Heart of Advaita as the totality; reality and the whole.
As the witness, the world is still viewed as an object and that object is unreal. For the formless witness, the delusion of the ego has been eliminated, yet suffering still appears, with no one to suffer. The witness always has an object, so duality persists and therefore so does suffering. The perception of an object indicates that there remains a subject (the witness) and this perpetuates the appearance of suffering due to continued separation.
As the Abolute and its power of consciousness, the world IS the ultimate reality, yet only right now and not absolutely; dependent upon, no longer an object, yet no longer unreal.