Nope you are not paranoid. I’m self employed and I’m in and out of restaurants all the time to service them. I see the areas that the customers don’t see.
Some restaurant owners are just nasty, they cut corners by skimping out on proper cleaning and many hire foreign workers (to save money) who may not be properly trained or up to date in basic hygienic standards.
As far as fast food, you can forget it because this is what could be going on, late at night, at YOUR local fast food chain: