I feel like this is a different version of the ‘reincarnation’ troupe, like in all the others they remember all their past memories or the memories are somewhat blurry. But just like in real life (if you believe in that sort of thing) you’re not supposed to remember, so our MC for some reason does and thinks that’s his reality but from reading Ch. 6 it seems like he was in an accident and Died. And his mind can’t cope with living his reality and remembering other memories, it’s like putting his brain in a blender or something and so the harder he tries to remember the more painful and dangerous it becomes. To the point where he’s bleeding drastically from his nose and having Seizures.
It’s actually the first time that I have seen a Manga that has portrayed someone who remembers and because ‘they’ remember it’s causing dangerous side effects. It’s actually quite refreshing, if that’s what this Manga is entailing.