"Brain fog" is a more commonly used term, although no doubt people experience different things and would describe them differently. For me, it's a weird feeling of vagueness, and to what extent varies significantly. Sometimes it's hard to focus and do work, but not always. Usually it's just like everything is sort of "passing me by". You wouldn't know talking to me, I function just fine, so maybe it mostly just affects my perception of time and/or memories. It's subtle and weird.