Swami Vivekananda's experience
"I saw with my eyes open that all the things of the room together with the walls were rapidly whirling and receding into an unknown region, and my I-ness together with the whole universe was, as it were, going to vanish in an all devouring great void. I was then overwhelmed with terrible FEAR. I knew that the destruction of I-ness was death, I thought that the Face of Death was before me, very near at hand. Unable to control myself, I cried out loudly, saying, 'What is it you have done to me?'
Laughing loudly at his words, Sri Ramakrishna touched Narendra with his hand and said, 'Let it then cease now. It need not be done all at once. It will come to pass in course of time.'"
Also check http://www.spiritualteachers.org/merrell_wolff.htm
"All human beings should try to learn before they die what they are running from, and to, and why."