Oh, my! The first time I saw this it was due to a cat under a severe nervous condition and it was a stress-relief thing. (Home being renovated and workmen in and out all day; her meowmy was traveling and only a pet sitter (me) to pay attention to her. It wasn't enough. )

Others have cited allergies and parasites. Fingers crossed that it's an easy fix.

You mentioned she'd been into the vets a lot lately. Could that be a stressor?