Much of being a physician is pattern recognition - the vast majority of Bell's Palsy is idiopathic (generally viral), and thus that's how we usually treat it. If we tested everybody for everything everytime the health system(s) would collapse.
It definitely helps as a patient to advocate, and add anything that a physician like myself maybe wouldn't always ask, like if you've been a tick-infested area and/or discovered a tick attached to yourself recently.