Definition: Bell's palsy is a dysfunction of cranial nerve VII (the facial nerve) that results in inability to control facial muscles on the affected side.
Bell's palsy is defined as an idiopathic unilateral facial nerve paralysis, usually self-limiting. The trademark is rapid onset of partial or complete palsy, usually in a single day.

Causes: brain tumor, stroke, skull fracture, chickenpox, mumps, neurological condition caused by chronic disease (e.g., diabetes, Guillain-Barre syndrome) and Lyme disease, Some viruses are thought to establish a persistent (or latent) infection without symptoms, e.g. the Zoster virus of the face[2] and Epstein-Barr viruses, both of the herpes family.
Symptom:
• facial weakness or paralysis,
• a dry eye or mouth,
• problems tasting,
• Dizziness
• Drooling
• Dry mouth
• Facial twitching
• Hypersensitivity to sound
• Inability to blink or close the eye, tearing, and dry eyes
• Impaired sense of taste
• Impaired speaking

Physiotherapy:
Electrical stimulation for muscles
Massage
Exercises
Self help:
Bell's palsy may make it hard to close your eyelid. If this happens to you, you could try using the following to help stop the surface of your eyeball drying out:
• an eye pad or tape to keep the eye closed before you go to sleep
• artificial tears (eye drops) to keep the eye moist
Ask your pharmacist for advice on eye drops if you think that they will help you. Tinted sunglasses may also be helpful.
• Try to blow the balloon
• Eat chewing gums
• Try to do all the facial expressions in front of mirror Remember to keep your mouth and teeth clean, as food can become trapped in your mouth.