According to Prof. Anil Seth (Professor of Cognitive and Computational Neuroscience at the University of Sussex) our brain hallucinate ALL the time. The hallucination we all agree on – are called reality.

"Billions of neurons in your brain are working together to generate a conscious experience -- and not just any conscious experience, your experience of the world around you and of yourself within it."

Youtube: https://www.youtube.com/watch?v=lyu7v7nWzfo

This kind of reminds me of a quote from the late, great TM.

"We are caged by our cultural programming. Culture is a mass hallucination, and when you step outside the mass hallucination you see it for what its worth." - Terence Mckenna

I was thinking earlier that maybe to perceive something we might have to already have it pre encoded into our whatever allows us to perceive. Just a random what if thought.

That quote doesn't specify what happens when you leave that mass hallucination. You trade it for another one? I realize that at least one learns to take less hard on the given first one, because it's kind of debunked. I can't fill in the dots what happens next, but it's like realizing Santa doesn't really exist
Yet with spice a kind of new Santa's come into place, a loooot of them

Nick Sand somewhere said:" If you're afraid getting delusional, don't bother because you were already delusional." or something like that.

It connects to what Yumi suggests, you can't (or its difficult) to really escape making projections about where you find yourself in, independent of encountered format.

Smells like you just trade bins you tap out of, new substrate to make projections with. Or you find different layers within the same bin that you are.

Funny suggestion, not new though: God was lonely and hallucinated him/her/itself into a differentiation. That makes me is you is connected to all. I think he's (or I for that matter) is kinky at some level
Related to OP: the group hallucination is just God hallucinating. Wondering how his pipe looks like

well yes this quote doesn't specify what comes next but i think his answer will be like you said you trade in for another one, his way of dealing with this is not to believe in anything... don't fall into the trap of belief..
listen to this if you haven't before all the way to 2:27:00 "...and thereby maintain the integrity of one's own soul and spirit... yet from it all i have learned that there is no religious revelation more satisfying than the hard one fruits of simple understanding"

You are right, my apologies in not clarifying, that quote doesn't precisely pinpoint the felt experience of leaving a mass hallucination. It just reminded me of the initial, threshold-stepping stone, so to speak, before any full-blown(alienated?) departure.

And yeah, that's true. In realizing that something doesn't actually exist(such as a narrow, temporary and strongly held belief) and perceiving that freedom of thought outside or within the group. Initializing some kind of breakthrough or further breakthroughs. Leading only to moar questions rather than answers. I resonate with Sand's quote. If I could slightly re-iterate what Nick Sand has said-if you're afraid of asking questions outside cultural 'normality;' don't bother being afraid because the answers will only connect to moar questions inside your 'normality.' To the degree that those 'delusions' will somehow untangle/re-tangle onto novel alterations in what we experience as consciousness. Through not believing anything leaves the door wide open for moar considerations and experimentation.

I'm entirely not sure! But the plant kingdom and other similar systems have some leverage in helping us discover our deepest, potential spaces of experience.

Haven't watched yet, but what group agrees on certain hallucinations? Isn't the group itself hallucinated?

So in the end it isn't even a collective hallucination. Or rather, the only thing collective about it, is that we collectively hallucinate, that our hallucinations are collective.

5-Hydroxy-Tryptamine is a helluva drug.