Palsy
It is not a myth, often times if you shock your body or parts of it with a brusque change of temperature, from very hot to cold, you will suffer a small stroke which will cause you to have partial and temporary or permanet paralysis of part of your face, often time making your mouth kind of crooked, It has a name which at the moment I do not remember, it is some kind of palsy.
usually the cure was to place a whole nutmeg for a prescribed period of time in the side of your mouth. Please be aware, that this happen more often in the tropics because of the climate, but it does happen here in the us too. so never open a fridge or walk into a walk in box if you are hot from the kitchen or just came from 100 degree weather outside.