CONSCIOUSNESS IS ON A COLLISION COURSE WITH THE UNIVERSE
Individuated human self identity - the "I" in "I" am - feels like a distinct self-aware identity passing through a succession of moments in time. It is the locus of spatiotemporal limbic experience parsed through the intelligent brain-prism of the cerebral cortex. It arose through genetic natural selection, evolved an increasingly complex substrate of associative memory into a mostly reciprocal symbiosis.
The "self" is convincing to "itself" because the input and output of the brain-prism is seamlessly normalised tick-by-tick into a coherent feeling of familiarity and stability and order; as opposed to arbitrary non-persistent intelligence, conceivable in an advanced computer for example, which has stability, order and capacity but no functional self-awareness.
Intelligence that includes the "self" as distinct identity can be called human consciousness. It's the gestalt by-product of a mind that's born of nature with a feeling of egocentric agency, trained by nurture to habituate a sense of ownership of local brain and body real estate. The mind is a construct of the brain but its roots predate and precede self-awareness, defining an operating system in which identity resides.
Instead of accepting the brain's own self-serving (but extremely useful) story of consciousness as a servant of identity that's personal, autonomous and persistent, consider instead the reality of consciousness in the context of a staccato frame-rate child-process of the brain.
Try watching the filming of an old TV screen and you'll see the TV flicker revealing the frame rate of the evolving interlaced image. If you'd been watching it in person, the same image would have seemed to interlace seamlessly, uninterrupted. The eye and the brain conspire to weave an unbroken visual story. It's no different in the mind, where conscious identity seems to be experienced as an unbroken succession.
This child-process of the brain feels continuous because the memory from which it is spawned is ontologically persistent and the experiential crucible is spatiotemporally consistent - and therefore predictable. That is to say, the brain operating system has the toolkit to assemble identity (or succession of identities that happen to be extremely similar) and this functions as a useful component of the cerebral ecosystem; a genetic capability for self expression that's trained into a unified voice by epigenetic experience.
Respawning identity is like vision, however, where one actually spends a lot of time functionally blind but the conscious experience one "lives" doesn't flicker on and off. The brain fills-in gaps in the very existence of the self from one moment to the next, just as it fills-in the moments of blindness to create a continuity in wakeful vision.
The brain run-level works much faster than the minimum frame-rate needed to keep respawning quotidian conscious identity. It ensures the child-process "self" includes, instantly on execution, near-absolute conviction of autonomous agency interlaced through an analogue of a physical present and an abridged "remembered" past. This would be perceptually indistinguishable from the brain's go-to fairytale of an objective continuity being authentically perceived by an independent autonomous self.
In short, our brains, as they subconsciously parse, analyse and represent the anthropomorphic lived experience, construct identity at a faster frame-rate than can be perceived by the conscious self (in an everyday sense) so self-aware identity manifests as a continuous phenomenological experience. But it isn't!
Given the fact identity formed by the brain must be convincing and robust if interrogated (by itself most of all) it's not surprising many familiar psychological phenomenon develop as practical daemons in all brain operating systems e.g. cognitive dissonance, denial, defensiveness, "rightness" conviction and so on. The brain has many resources available to ringfence the identity processes it spawns.
As with any incredibly complex organic super-system, the human brain does not always function perfectly or with absolute consistency. The safeguards and redundancies are legion but this is not always enough.
Psychological conditions like schizophrenia, while rare in extreme cases, are unsurprising features of this brain-spawned quotidian identity and though occasions where one might perceive a blip or disconnection across one moment's identity and the next aren't so rare, long periods of multiple personality without cross-identity awareness would be sufficiently dangerous to let natural selection breed out the extreme cases. Multiple personality brains with cross-identity awareness are less rare but inconvenient enough to bias in favour of a dominant (more regular) personality so as to habituate others out of conscious airtime. Some breakdowns can be the result of just such suppression, especially in times of stress where brain resources are stretched and there's less processing time left to keep a particular "self" in splendid isolation.
Drug experiences, usually precipitated by the "self" in an act of wilful risk and empowerment, force the brain to shuffle and shift limbic and spatiotemporal perception. The toolkit of self-awareness tries to stay running regardless, levelling out the neurocognitive turbulence while the body works to purge the alien chemicals from the bloodstream.
Psychotropics blur the ring-fencing so the "trip" is invariably familiar and fascinating, authentic and transcendent all at the same time; and most importantly retained in some form accessible to the sober everyday identity.
Meditation, another expression of "self" will asserting against the brain’s operating system habit of ring-fencing, can shift the interlacing of the untrained (normal) mind to focus away from the passive reaction-thoughts of undisciplined everyday experience, initially through techniques but eventually through what is optimistically termed transcendence. This shift in perceived awareness away from conscious chatter allows access instead to the gaps in the identity frame-rate. This can ultimately resolve into conscious experience without a continuous self.
Indeed, this disentangling of the self and conscious experience becomes a technique of dissolution because, subjectively, gaps in the frame-rate of consciousness are times the brain isn't projecting an identifiable self, so though conscious awareness persists, it's no longer a simple self-awareness bound up in a distinct egomaniac identity. It becomes possible to exist outside of the storyboard ring-fencing. This can be liberating, depending on one's individual narrative and what external conditions are being imposed. It can be calming, helpful in the maelstrom of habituated everyday life. It is certainly self-empowering.
Dissolving or manipulating the conscious-self, through mediation or drugs or dissolution by medical condition doesn't necessarily change the gestalt reality of the mind. Nor does it redefine the brain's fundamental experience - past or present i.e. what gets parsed into memory as you move forward in space-time. Identity is, after all, just a child-process of the mind operating system in the wetware of the brain. What's in the brain can affect the emergent self but may also be kept separate, according to the baseline specifications of identity creation.
The "self" as one perceives it, from one moment to the next, is not an inevitable succession of moments in a single story of life experience. It is a "self" respawning with the turn of every page, a high-level feature of your mind but not independent or autonomous or omniscient (within its own environment). The brain has so many more resources than emergent conscious identity - the “you” - and the mind so diverse an ever-evolving mandelbrot meta-landscape, to have explored it every waking moment for a hundred years is a lifetime that ends with more to discover than existed at the start!