A first definition of this complex phenomenon, and perhaps the least hazardous, will be shamanism = technique of ecstasy.
Mircea Eliade, Archaic Techniques of Ecstasy
I will always highly recommend this book, but will make a small point of clarification. I do believe that “ecstasy” may be the wrong word, and maybe this can be chalked up to English not being Professor Eliade’s first language. Because in a modern sense, ecstasy has connotations of pleasure which is not always the case. Many of these techniques involve discomfort and outright pain. From an Asian perspective the word ecstasy may have some validity in that from a certain Taoist point of view, all experiences can be judged pleasurable in the mind of the participant. But I think what comes closest is the chaos magick definition of “gnosis.” Which is, of course, a borrowed word itself and not entirely synonymous with the original meaning of the word. So English really doesn’t have a good term for what is being described, which in a general sense encompasses all altered states of consciousness.