DMT is an odd one and not for the faint od heart. It's funny you mention such a dark experience today, as i was just reflecting on a "troublesome" looking entity that wandered my way that I sort of forgot about. They didn't seem to be quite main theme of my experience, though they did wave a sort of feathery (but they weren't feathers) "talisman" over me before things got real interesting
As for what occurred in relation to your friend, there's a lot of explanations that could be possible, and almost all of them are impossible to prove in any conclusive way. Sounds like they were altered too, and you could've influenced each other's trip simply by miniscule microresponses to the hyperspatial stimuli. One ought not to rule out mirror neurons. There could've have been some sort of movement of separation that could've been tiny, but you both noticed it tremendously. And... it's also possible that entities could've been toying with you both...
It's hyperspace; it gets real.
What is your experience with other altered states?
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