Harry who is Plagued by nightmares from his own past which supposed to be his present that is now his future because he is slowly forgetting the events that led him to be in his enemy's past because these events still didn't happen and maybe it will never happen so he writes his thoughts in a book making different sections one for "definitely happened" two for "partially happened doesn't remember the rest" three for "vague information like Ron's favourite colour" four for "indefinite feelings maybe happened maybe exaggeration" five for "feelings and thoughts kind of judgements that he doesn't remember its reasoning" and so on ....
Then days pass and he starts to be less plagued, "Potter" last name does make wonders "shelter" "money" "relatives" "connection" and "fun" and he changes and starts to be "Harry Potter of 1940s" more than "Harry Potter of 1990s"
But still religiously from time to time Harry gets nightmares and he still reads the book he wrote to remember and determine the context of now his "present" so he gets disturbed by the fact he changed beyond intention because of time effects
So he withdraws becomes anti-social observes more and is more paranoid and looks for ways to protect his own book for example like "dark magic" and in a way he isn't only preserving relative information but also his own very private identity... In a way he becomes similar to "Tom Riddle" making himself problematic skitchy ruthless and lonely....