I had an ex, who would get brain fog: much smaller working memory, impaired executive function, and sluggish thinking in general, every time there is some kind of emotional vulnerability being shared. Pretty much any highly emotional event can trigger the ex into this mental state.
This vulnerability hangover is quite similar to POIS, as in it peaked the morning after the trigger: It is usually the worst when one wakes up in the morning the day after. and it takes 2-3 days at least to fade away.
I suspected it has to do with cortisol-induced cytokine issues. And anecdotally, celecoxib (before or after) or propranolol (before) seemed to alleviate the issue greatly. at least to my ex.