Hallucinations are pretty concretely defined, medically. Seeing stuff that isn't there. Hearing stuff that isn't there. Things moving when they aren't.

For me, the psychedelic experience is more about the "Ah hah! we're all in this together! We're all the same thing! I've removed the veil and barriers I've built up all my life and can finally see clearly what it's All About." I'm sure it's different for others, but I don't experience that "oneness" or "connection" on dissociative. It feels like I am born again, free to be vulnerable and experience the world without the lenses that society and myself have placed over my eyes.