Bieber shared on Instagram,

“Obviously, as you can see from my face, I have this syndrome called Ramsay Hunt syndrome, and it is from this virus that attacks the nerve in my ear and my facial nerves and has caused my face to have paralysis.”

As seen in the video, Bieber is suffering from partial facial paralysis, in which he is unable to move his nostril, smile, and blink on the right side of his face. According to WebMD,

“The virus that causes chickenpox (varicella-zoster) hibernates inside groups of nerves. It can stay there forever and never cause trouble again -- or it can "wake up" and create a new infection in one of the nerves in your body.”

Fortunately, Bieber was diagnosed early so, with proper treatment, Ramsay Hunt syndrome should resolve itself in a couple of weeks. In the meantime Bieber assured his fans,

“I’ll be using this time to rest and relax and get back to one hundred percent so I can do what I was born to do.”