How can using a fan while you sleep cause Bell's Palsy?

HOWEVER, cold trauma is known to give advantage to many viruses in entering the nose, lungs and likely ear canal... and, asleep, it's harder for the body to warm the ear as fast as the wind is cooling it.

Flu, varicella and herpes virus abound, so ear-canal trauma cannot responsibly be ignored as the most commonly mentioned precipitating event ... wisely deemed a risk, setting up a "perfect storm" for Bell's Palsy.

Hi,
Using a fan, while sleeping or while awake, does not cause Bell's palsy.
Bell's palsy is a disorder of the nerve that controls movement of the muscles in the face. The cause is often not clear, but herpes zoster infection, HIV, Lyme disease, middle ear infection and sarcoidosis are possible causes.