Has anyone else experienced unironically getting dumb rapidly? I feel like I've become a fucking idiot in the last two weeks.

>My work is fairly menial but I've 100% started having trouble remembering basic things or having to take extra notes/double-check my notes to remember things
>Taking a long time to "understand" things when I read them or someone says them to me
>If I read lets say a news article I'll forget the information it had contained
>Short and medium-term memory is fucked, but I seem to be able to remember things from months or years ago with decent precision (or maybe I just think I do)
>Terrible mood and as a result I'm extremely frustrated about becoming a total idiot

I was never a genius or anything but my mental capabilities used to be so much better than they currently are. I'm not trying to be a hypochondriac or whatever you want to call it.

Is this carbon monoxide or a brain tumor or what can it be? My biggest fear is that it's irreversible already (seems like cognitive-related issues are, other than fairly acute things like being drunk/high or intoxicated on some sort of poison).