This is a fascinating post! Thank you for sharing your story.

And this is where the trouble started: I really couldn't put the book down. It was as though the mental stimulation afforded by ZAMM had pushed me over the lip of an energy barrier, and I was now in an incredible downhill rush.

This ability to dissociate from the rest of reality and focus on one thing is a gift! Albeit scary if you feel unable to stop focusing. I've felt it occasionally while working on novels, but in general I have to expend mental effort to focus on something, and I think that's true for most people. You're lucky in that it's probably easier to learn to control this focusing ability when you have it automatically than to learn how to activate it in the first place.

I'm told that Bertrand Russell was once asked: "But haven't you ever had any mystical experiences?" "Why, yes," he replied, "I ignored them."

That's basically my current perspective. Then again, my mystical experiences (usually triggered by singing church music in a group setting) are not particularly useful in an instrumental sense; they bring warm fuzzy feelings and a sense of oneness with the universe, and glimpses of 'inspiration', but I end up having to work just as hard to flesh out those inspirations as I would have anyway.

I would like to read further posts as it would be interesting to see if I have your capacity to get lost in 'arational' focus; terrifying as it might be, it's new ground to explore and that's tempting.