Dudley Moore is battling a rare brain disorder
Moore is suffering from a rare brain condition called Progressive Supranuclear Palsy (PSP). It attacks brain cells which control balance and eye movements, as well as some mental functions.
"It's totally mysterious the way this illness attacks, and eats you up, and then spits you out," the 65-year-old actor and musician told BBC One's Omnibus programme.
"There's always this feeling of why did it hit me? and I cannot make peace with it because I know I am going to die from it.
'Music is my main comfort'
The documentary, Dudley Moore: After The Laughter, focuses on the one true love of the performer's life: his music.
It reunites the star with a composition for a string quartet which he composed as a student.
The documentary was filmed in Nova Scotia and New Jersey and shows Moore working to recover his lost music.
"Music is my main comfort now," said Moore.
"But it's difficult to know that all the keys are there to be played and I can't play them. People started saying I was drunk on stage... it was dreadful."
Household name
He was born in Dagenham, Essex, in 1935 and first came to public attention in the early 1960s with the Beyond The Fringe show, together with Alan Bennett, Jonathan Miller and Peter Cook.
The four men concocted a review show of loosely linked satirical sketches.
Moore and Cook's subsequent television shows Not Only... But Also saw them become household names.
Moore then went to Hollywood and became a star after the 1979 Blake Edwards' film 10.
Two years later he earned an Academy Award Best Actor nomination for Arthur.