Mysticism
A mystical experience is an experience of merging with God ot the 'cosmic spirit'.
The idea is that what we usually call "I" is not the true "I". Some mystics call it God, others call it the cosmic spirit, Nature or the Universe. When the fusion happens, the mystic feels that he is 'losing himself'; he disappears into God is lost in God in the same was that a drop of water loses itself when merged with the sea. Your real 'I' - which you can only experience if you are able to lose yourself - is, according to the mystics, like a mysterious fire that goes on burning to all eternity.
People of our own time who do not adhere to a particular religion also tell of mystical experiences. They have suddenly experienced something they have called "cosmic consciousness" or an "oceanic feeling". They have felt themselves wrenched out of Time and have experienced the world 'from the perspective of eternity'