What is Ramsay Hunt Syndrome, rare condition that paralysed half of Justin Bieber's face?

Justin Bieber revealed he has been diagnosed with Ramsay Hunt Syndrome, which has paralysed half of his face. The syndrome is a neurological condition caused by varicella zoster virus. It occurs when a shingles outbreak affects facial nerve near one ear. Its symptoms include, severe pain in ear, painful rash on eardrum and weakness on one side of the face.