Were they hockey fic? The only time I've seen it is in hockey fic deailng with RL concussions on the field, and I only ever read hockey fic for the tropes and never kept track of it very well.

I've read a fair amount of sickfic that does various illnesses/injuries realistically, but in non-sports fandoms at least, concussion fic is so vastly outnumbered by "walked into a bar, got unrealistic amnesia". Or "needed to be knocked out for plot reasons, no side effects" (which is. Fine.)