It is certainly the case that there can exist an atheistic mysticism, a mystical experience naked and not clothed in any religious garb. - Walter Terence Stace

The most important, the central characteristic in which all fully developed mystical experiences agree, and which in the last analysis is definitive of them and serves to mark them off from all other kinds of experiences, is that they involve the apprehension of an ultimate nonsensuous unity in all things, a oneness or a One to which neither the sense nor the reason can penetrate.

If God does not lie at the end of any telescope, neither does he lie at the end of any syllogism. I can never starting from the natural order prove the divine order. The proof of the divine order must lie, somehow, within itself. It must be its own witness. For it, like the natural order, is complete within itself, self-contained.

Mystics more often than not avoid direct reference to themselves.