The works of this phenomena are far from understood really, but one can imagine the bearing impact of neurotransmitters, hormones, molecules etc in the process of giving ourselves this experience of real time reality. ..One could argue that our specific senses pick out their own preferred "slice of the stimuli cake" in the space surrounding us, creating ONE version of the possible interpretations of the same "reality".
So if I can, at least, accept the notion that our perception of reality is produced by selecting information in the environment in an algorithmic way based upon the neurological/chemical environment in the brain and CNS - I can also be open to the fact that the experiences one can have by altering the chemical preciseness of the brain - are simply a product of different "slices of the same stimuli cake" we all live in. ..And in other words also real, and not real at the same time. As in quantum. But with this "conclusion" comes the fact that altered states actually could be as real, and not real, as this reality we share. I am ofc only thinking out loud