I got Bell’s Palsy from stress a few years ago. It was awful. Fortunately I mostly recovered, but some people get permanent nerve damage. It’s not always just one side of the face. I still have to use a straw to drink out of a glass and when I smile too big, my eyes look uneven. But some people lose the ability to smile at all.

It sounds like only a cosmetic problem, but it ruins social interaction to not be able to move your face. Facial symmetry and small movements in facial muscles are bigger parts of human communication than people realize.