I think altered states are a spiritual phenomenon but you can say biology and pathology has its influences on these states. One interesting way of thinking is that our waking lives are experienced from a very low state of awareness as we go about business and getting things done each day. When we sleep, I believe we actually experience ourselves fully and our sub-concious/un-concious minds emerge letting us explore our fears, needs, desires and to make aware of life lessons that are presenting themselves both right now and in the future.
Another way of looking at it is that when we are concious, we are just experiencing ourselves from a top-level - like the last stone on the top of a pyramid. We are aware of a limited amount of information. When we are fully aware of our sub-concious and un-concious minds ( when sleeping ) then we are revealing the rest of the stones of that pyramid below. These stones are memories and past experiences and knowledge but also the rest of who we are as a being.
I believe that altered states of awareness are just that, going down to different levels of conciousness within ourselves. But what I describe above sounds like normal conciousness is actually us asleep and when we are asleep we are actually awake as ourselves completely.
I have got that train of though from a Coast to Coast radio show video on Youtube I watched recently and it resonates well with me. Interesting that word "resonate" as in "vibration" and like vibrations attract spiritually

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Now I need a

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