On the Secular Web Kiosk is an article Confessions of a former mystic by Edward Tabash, talking about his past experiences with Kundalini Yoga and similar forms of mysticism. He believes that mystical experiences have a biological root.

A completely reasonable hypothesis -- it would also account for why the "revelations" in mystical experiences are

1. variable
2. lacking in information of truly external origin

I mean by 1. that different mystics experience different things. Hindu and Buddhist mystics generally do not experience the Virgin Mary, for example.

And I mean by 2. that such experiences don't contain information that the experiencer would be unfamiliar with, such as speaking in languages that the experiencer had not had any experience with. Or mathematical concepts and theorems that the experiencer would not have known about.

As to point one, that would be due to cultural influences..not biological. If it is strictly bio you Would expect similar experiences.

As to point two, these things have been reported in various places..at least some knowledge and languages..don't know about theorems..can't imagine that being too important to mystics.