@Curzelake
Spoiler!
Sadly it was rushed in the novel it just explained that after resignation from his company he drank alot and met a some kind of Granny who explained that he was living in a fake world and he was a protagonist in the real world and gave some kind of potion which brought him to the real world and he forgets that it was Granny who sent him back to the real world that's why he has no memory what happened to him at the beginning chapters of the manhwa
☆(ﾉ◕ヮ◕)ﾉ*