My parrot is regurgitating violently

by Tanya Tanyeli
(UK)

Hi,
My parrot has been shaking his head very violently. In the past he would eventually throw up a white ball, but this time i only saw the ball before he swallowed it yesterday and has been violently shaking his head and nothing comes through. Its the worst i have seen him do this. What should i do and what do you think it is?