Bell's Palsy, aka facial paralysis, describes a temporary paralysis of one side of the face caused by trauma or infection of the facial nerves. It usually affects only one side of the face at a time but in very rare cases can affect both sides simultaneously. The damaged facial nerves don't allow information to pass from the brain to the face resulting in facial paralysis. The condition is marked by a drooping of the affected side of the face with the eyelids and mouth having a sagging appearance. Eyelids typically don't blink together because the affected eyelid moves more slowly than the other.
In extreme cases the eyelid cannot move at all and eyedrops are used to moisten the eye. The cause of Bell's Palsy is ultimately unknown but believed to be caused by a virus that damages the facial nerves. Typically treatment is a combination of antiviral medicines and steroids.