For whatever reason, my smile has normally never been straight. I deliberately try to yank up on my right side for photos, knowing that otherwise, it will look like I'm having a stroke.
BUMP!
To the best of my knowledge, no one’s face is exactly symmetrical. Just that if someone you know at work, or at home, cannot smile in their usual normal way—straight, lopsided, or whatever is normal for them, it could be a sign.
As I mentioned, this is just basic first aid. Nothing substitutes for a competent medical examination and treatment.