Funny that you ask this. I recall reading about this a while ago although I can't find what I was reading. Apparently this is called "ego suicide." Killing your original self and letting the personality you created takeover your entire being.
I have an further question. No pressure if you don't remember or it wasn't listed. (I'm really interested in anyone who can answer this)
Is there a term for when you believe that that "original ego" was killed by something else? Be it killed by "the world" or some serious life event or revelation or something.
Looking at the wikipedia page, I'd say "ego death" sounds like a very different concept.
What the parent posters are talking about is when you have two personalities: the original and the mask, but the mask stays on so long it becomes the new permanent personality. The original "ego" is gone and already replaced.
"ego death" sounds like a loss of the only personality. There's no alternate.