The realization, which one has in Self-realization, is not an experience. And, contrary to being a "knowing," it is an un-knowing. 

The reason why this can be said is because Self-realization is merely a profound insight into the total and complete absence of limitation. In other words, it is entirely outside the bounds of both experience and knowledge.

In fact, to the Self-realized, the word which comes closest (to the condition described above) is nothingness.

In actuality, it is not a matter of "knowing Oneness" or "experiencing sublime consciousness." It is an irrepressible realization that the ultimate condition is of no-thing; nothing. 

In other words, in this absolute awareness there is not any thing about which we suppose we will be certain, as a conceiver knows a concept. 

It may sound peculiar, but this is the Self-realized state.