I know half a dozen possible ways in which 'unusual' experiences can happen that do not require mystical, metaphorical or metaphysical explanations.

Yes, I realize this. Your explanations are some of the possible "ultimate cause(s) of these experiences". As are the things others of us have described. Obviously you don't have to accept what others regard as being ultimate causes of anything.

Personally, I use the word "believe" as a preface to my descriptions of what I consider to be "reality" because "I believe" that none of us can really prove anything. Not even that we, in fact, exist at all. So as far as I'm concerned, everything we hold to be "real" is based on belief.