Quick disclaimer: Sorry, if my phrasing is not accurate, English is not my first language (and the stories I write are not in English).
I am currently writing a short story that is giving me headaches about the status of the narrator (or point of view, not sure which term is more accurate). Without getting into the details of the plot, the main character (Alice) is gradually being metamorphosed into a markedly different character (Bob) as the story progresses. By the time the story comes to an end, Alice has forgotten about her former self and her recent adventure; she is now fully convinced to be Bob.
Here is my problem: I really want to write this in first person, internal narrator. It would allow me to express the gradual change in mindset much more smoothly and naturally. The tone is also along the lines of thriller/horror, with some tense moments of panic, which I would prefer to write in 1st person as well (and ideally present tense, though this is both less important and less problematic).
However, it doesn't make logical sense to me. This is a question that often occurs to me when I write a story: Where the hell is this story even supposedly coming from? Surely Alice was not taking notes while she was in the middle of her stressful adventures. Surely, once she has fully become Bob and remembers nothing, she cannot tell her story. So who the hell is telling that story in 1st person?
Is it impossible to write it this way without creating a paradox? I feel like having to rewrite the whole thing in 3rd person would really be a waste, would weaken its impact, as well as make it seem a lot less natural. An external narrator transcribing the gradually changing internal thoughts of Alice would feel artificial to me. Having to write this without access to internal thoughts would be even worse, at least for my level of written expressivity.
What solutions do you suggest to solve this somewhat recurring problem that I face whenever I try to write 1st-person style? Do you always have to justify that the character actually physically wrote the story in that case (or at least would have been able to do so)?