The Only Fools And Horses star, 82, told BBC Breakfast he caught the virus in July after staying well during the height of the pandemic.
He said: “I got it seriously bad. Because all the muscles weren’t working, I collapsed and I fell against the radiator… I was so weak, I couldn’t get up.”
Sir David said he had attempted to go to the toilet.
“I crawled to the bed,” he said.
“The muscles weren’t working and I used the bed to try and stand up so that I could go to where I wanted to get, and also get back into bed, and I couldn’t…
“I tried for about a quarter of an hour, trying all sorts of things to stand up so I could walk about.”
Sir David said he made “walrus” movements to move towards the door before he was discovered by his wife.
The actor is best known for playing wheeler-dealer market trader Derek “Del Boy” Trotter in classic sitcom Only Fools, as well as DI Jack Frost in crime drama A Touch Of Frost.
His other TV roles include Granville in Open All Hours and Pop Larkin in The Darling Buds Of May.
He is publishing a Christmas book featuring stories from the making of the Only Fools festive specials.