is coding amnesia a thing? i ran into an error few weeks back and today when i ran into it i completely forgot any knowledge i had of it

Are you under heavy workload or stress? Personally I've experienced this in such situations or when lots of projects came and went.

It is completely normal.
That is why important to have clean code and self documentation of the code.
90% of time is wasted to re read the code.
We don't just document code for others, we document for our future self too ;)
the choice of variable names and functions should be careful.
Think if u can guess in two months what it will mean ;)

In two months I usually forget everything completely.
That is why I automate all processes with CI CD pipeline.
It serves me as self documentation how to build, test and Deploy the repo.
Plus removes the routine operations ;)