"In Jewish mysticism, it is not always understood that union with God is but a temporary experience. Hence, there are warnings against allowing oneself to be dissolved into nothingness due to an assumption that returning to the state of a separate existence is not a subsequent step. But clearly in the above passage, it is accepted that at least some do come back to their former separate being."
That's an excerpt from a chapter titled "Ethnohermeneutics II: West," from a book called The Mystic Experience: A Descriptive and Comparative Analysis, by Jeshua ben Yosef (Jordan Paper), 2004.
And the passage referred to as "above" comes from A disciple of the Great Maggid, Levi Isaac of Berdicheve, who wrote in Kedushat ha-Levi:
When the Zaddik cleaves to the nought, and is [then] annihilated, then alone he worships the Creator from the aspect of all the Zaddikim, since no division of the attributes is discernable there at all.... There is a Zaddik who cleaves to the nought and nevertheless returns afterward to his essence. (qtd. in Paper)
Maybe this explains Levinas's reluctance to talk about religious experience? The author goes on to say, "In the main, the contemporary Jewish attitude toward mysticism, let alone the mystic experience, is to ignore if not deny its relevance within Judaism." Seems odd to me, given the nature of the stories in the Talmud, which practically all involve religious experience (Moses, Abraham, Noah, certainly). Even this seems like an insufficient reason to ignore the testimony of those who claim to have mystical experiences. Certainly most religious traditions have warnings: my Kundalini Yoga DVD comes with a warning that says, basically, "Careful: you might not be ready for this," and mainstream Christianity can hardly be said to encourage mysticism -- indeed, Philip K. Dick wrote his best books understanding that admitting to mystical experiences might land one in the nut-house.