Essentially, there's a part of your brain dedicated to telling the difference between you and not-you--it's used for proprioception and balance and such--and that part of the brain is almost always active. But it goes way quiet when people have intense religious experiences! They tested it in Buddhists doing their zen thang and in Franciscan nuns chilling with God, and found the same neurological responses. The you/not-you divide gets less distinct, resulting in that nifty all-encompassing connectedness.

I totally feel you about imagery. As much as I love to wallow in biological explanations, I still sometimes use visualization techniques I picked up from pot-exuding old hippies at Whole Earth when I was a kid. If it works, it works.

I don't have a libretto, but I have the nice hardcopy CD with complete lyrics booklets, which in the case of a sung-through musical probably isn't far off from the libretto. I'll poke through it next time I visit you guys. :)