It's connected to the general subject of mental illness, but not so much this case or story brought up, but as chance has it I recently talked to two different people who experience relatively rare and extreme forms of mental illness. One experiences a number of distinct personalities, the other hears voices, which she doesn't identify as belonging to her central self. I'll share a bit about their conditions, which they both discuss openly online, but of course I'm not going to reference that.
I had talked to someone with schizophrenia before, who experienced some of the internal voices as not his own. The multiple personality case is completely different, in that different personalities could manifest at the same time, and share a mental awareness space, but another form of expressing distinct and not overlapping consciousnesses was also experienced. The personalities were developed enough to take up individual personas and names; that earlier contact was experiencing roughly the opposite of that, just as internal noisiness. She said that the cause seemed to be childhood trauma and extreme later life trauma, probably made worse by extensive drug use. She seemed pretty balanced about it all though, relatively comfortable with that form of experience of reality.
The other contact experienced a consistent, permanent internal self, but identified the other voices as external to that. They didn't seem to manifest distinct enough personalities to take up separate names and personas, but they may have been more consistent than we discussed. The strangest part, to me, was that she attributed these voices as mentally external, not as fragments of her own atypical form mind. That might be easier to accept and relate to. Then again it seems possible, just not the most intuitive or standard read, that the voices could be truly external, along the lines of spirits, or from another dimension, or something such. Most likely not, one would tend to think, but I tend to frame my view of reality as accepting conventional things as accurate and then leaving the rest a bit open. I don't know if ghosts and such exist, as an example, but I just don't worry about it, versus trying to draw a clear conclusion. I get it why lots of people like their reality much plainer and better mapped out.
A lot of times when I hear about extreme cases like these in experience it makes me wonder if most of the rest of us really experience that much of the same form of reality as it seems we do. Studies and reports on the degree of internal voice people experience varies, for example. I mean a relatively singular internal self, in the form of inner dialogue, nothing to do with mental illness and such. Internal consistency across a broad range probably varies a lot. I wouldn't be surprised if "mental health" isn't really as well defined as it might intuitively seem to be.