I was just giving an example as Bell's Palsy.
Yes, fish have facial nerves, but not like humans. Fish heads and faces are made of bony plates (most not all).
Who know if fish get Bell's Palsy? They can't tell you that half of their face is numb and they can't feel it. Half of their face doesn't droop, unless it is a bone disease or infection. So who is to know?
Does your puffer seem to be having a problem?
Yes and Bell's Palsy is neurology but in some casesa pinched nerve could have the same effect, as the example I gave.
"My friend had this and after he got adjusted it went away, 'pinched nerve'".