I've had Covid twice. Thankfully, I didn't get brain fog, but both times one of the early symptoms was a sudden mood change--I started feeling both angry and sad for no clear reason a couple of days before I tested positive (so it can't have been a response to the diagnosis).
My second bout of COVID is instructive. Physical symptoms have been mild but the brain fog is chronic and anxiety has gone haywire. This is what happened to me two years ago, triggering all manner of problems I’m still dealing with. (Mental illness as symptom of Long Covid.) 1/4