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Consciousness is often said to disappear in deep, dreamless sleep. We argue that this assumption is oversimplified. Unless dreamless sleep is defined as unconscious from the outset there are good empirical and theoretical reasons for saying that a range of different types of sleep experience, some of which are distinct from dreaming, can occur in all stages of sleep.
Pubmed Articles
Does Consciousness Disappear in Dreamless Sleep?
Sciencealert Article We Were Wrong About Consciousness Disappearing in Dreamless Sleep, Say Scientists
We have a good definition of “death”, it’s the irreversible stop of some activity. For a brain, that’s neuronal depolarization; for a body organ or cell, it’s destruction past its ability to regenerate.
The self, is a snapshot of a brain state at a certain moment, which is technically irreversibly disappearing 30 times a second, but we like to think of it as just “changing” and forming a causal sequence we call “consciousness”.
This threshold has changed over time. So I don’t think it’s a good definition of it hasn’t always been the same point.
And the rest of your comment is just philosophy. You’re neither wrong nor right. Definition of self is not a concept there’s really any consensus over.