Justin Bieber says a rare disorder that paralyzed half of the superstar performer's face is the reason behind his tour postponement.

The multi-Grammy winner is suffering from Ramsay Hunt syndrome, he said in video he posted Friday on Instagram. The syndrome causes facial paralysis and affects nerves in the face through a shingles outbreak.

Bieber's post comes after he cancelled his shows in Toronto and Washington, D.C. The singer demonstrated in the video that he could barely move one side of his face, calling the ailment "pretty serious."

"For those frustrated by my cancellations of the next shows, I'm just physically, obviously not capable of doing them," he said. The singer added, "My body's telling me I've got to slow down. I hope you guys understand."

Bieber said he's unsure how long he'll take to heal. But he appeared positive about making a full recovery through rest and therapy.

"I'll be using this time to just rest and relax and get back to a hundred percent, so that I can do what I was born to do," he said.

In March, Biebers' wife, Hailey Bieber, was hospitalized for a blood clot to her brain.