I was reading chapter 1 of chainsaw man again (Started 2 years ago) and it felt like I was reading it for the first time. Like I literally forgot that it was his father’s debt or that he sold his nut or even that it was the yakuza that tried to kill him. I know the very bare skeleton story, but I easily forget details in between.
Should I go to a doctor or am I overthinking it?
Go to the doctor immediately. Forgetting the plot points of the initial story arc of any manga is a genuine sign of IBS, which as we know can cause enhanced toilet awareness.