I don't really think you as a person exist until you have active memorable thoughts. Until you can articulate yourself and remember / understand what happens around you, you're still gestating imo.
I mean do you remember anything from when you were 1? You may as well not have existed for all intents and purposes, you can't live on your own, understand anything, or act on anything that you'd ever know you did.
Similarly is the person who wakes up with total amnesia really the same person that became afflicted by total amnesia? Or are you imprinting upon the new personality when you tell them all about the previous inhabitant.