Hi David,
Nice to be communicating with you. By "everything in existence would vanish" I didn't merely mean "my" thoughts or emotions. I meant literally everything in existence. If I remember correctly, there is a concept in physics that if any one thing was to truly vanish from existence, all of existence would implode, like air let out of a balloon. And so, I was referencing that tenet, a bit tongue-in-cheek.
I truly do understand the concept of no-self. I'm capable of deconstructing the illusion of my reality; my identity, my perceptions, etc. But understanding something intellectually and really experiencing or embodying it are two different things.
Sam Harris's meditation app has "theory" facets, but the main thrust of the introductory course is not lecture, but guided meditation.
It begins with focusing on the breath, eyes closed, and just noticing sensations, etc. Sam then suggests to keep eyes open, and experience the visual field as just shadow and light. So far so good.
But when, a few weeks into the course, he suddenly introduces no-self ("Now look for the looker," or, "who is there experiencing these sensations?") it felt like a leap. These suggestive phrases did not evoke sensations of selflessness in me. I did not suddenly feel a dissolution of self and a oneness with the universe. It felt too soon, too pushy, and had the opposite effect, further grounding me in my sense of self.
Again, I understand there is a possibility of consciousness without the "I." One of my favorite books is B. Alan Wallace's "Embracing Mind" in which he wonderfully defines substrate consciousness. For me, Sam Harris sort of smuggled in the no-self into an otherwise effective meditation app. It was off-putting, and when I researched it a bit, I found it was not only off-putting for some others, but some people had scary emotional experiences. It all caused me to question the safety and efficacy of teaching Dzogchen with an app, hence the article.
All the best to you.