I'd say it's mostly normal behavior: a very sensible desire to not be a weirdo, as being branded one can have bad consequences. But I suppose the more insecure one is, the more likely it is that this 'internal monologue' becomes a problem. And of course it can be argued that what is normal is not necessarily good or healthy :-).
My favorite (short) novel illustrating this 'meta-existence' is Notes From Underground. I read it in a period where I was very insecure and becoming more and more withdrawn. Seeing on paper my exact thought process and how it negatively bleeds into my (social) behavior and becomes a self-fulfilling prophecy was very confronting, and a great warning and incentive to snap out of it somehow.
I think the problems arise in a way similar to addiction: the 'meta' becomes habitual, then compulsive an overpowering, and is experienced as negative, perhaps even debilitating. But also gives a form of comfort. So we keep doing it.
A certain degree 'meta', of self-reflection is fine, perhaps even necessary in the complex societies we inhabit, but especially in bad times it can become an addiction, making those bad times even worse.
I strongly believe being alone is crucial for our mental health. Or to 'just be', I guess. And being 'meta' in your head is like constantly having conversations of sorts with yourself or with others. It's not being alone.
In fact, it's worse than being alone, because your mind can puppeteer all these others, so you really just end up projecting your insecurities and judgments back unto yourself, except with more authority, because you're imagining your partner, parent, boss, or friend doing it, which somehow makes it seem more objective and real and painful.
