I have this happen at times; I associate it with tiredness.
I've also noticed parts of my mind switch off suddenly when tired — one annoying and unfortunate thing I've inherited from my father is a tendency to get stuck in metal loops about imaginary arguments, sometimes involving people who died a decade ago, and one time this kept me awake… until just suddenly switching off like it was a part of my brain that fell asleep.
My understanding is that different bits of the brain do fall asleep separately than the whole, and that this happens at incresing scope and frequency the longer one has been awake, and knowing this means it wasn't scary to experience such a sudden change of mental state.
Medicine has a long way to go before it can deal with the qualia of post treatment life.
Not fun.
Is it impossible to don't afraid of anything?
Or maybe even scarier / more powerful: is it impossible to simulate it, adequately?
Be wary of applying double standards here.
Also, note that it says "the" mystic, whereas your claim is "anyone who". You also made broad negative claims.
Mysticism is often counter-intuitive, and imho "woo woo" isn't genuine mysticism.
I consider myself a bit of a "psychonaut" and occasional practitioner of meditation.
But I had to cultivate this appreciation. I believe the DR/DP was a manifestation of my self's resistance to a new way to see the world and a new way to relate with my self - or lack thereof.
I stopped resisting, DR/DP went away... easier said than done though, I know. And I'm sure my experience was unique to my own.
So too with DP/DR.