To add to that:
Why are people having these experiences?
Because there are chemical and physical processes (which we have evidence for) going on in their brain that other people do not have.
Why do some people have these processes and others don't?
Because these processes are either predestined to happen by genetic layout, or they happen because at some point in the growth process of the brain, a randomly occurring divergence creates structures which start these processes.
Why are many people who experience these processes religious?
Because they have been socialized to believe that if something like these experiences happen, they are a sign from God(s), or ancestral spirits, or demons (sometimes all of these, to separate "good" impulses from the "evil" ones).
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