The Little Britain funnyman starred alongside a mass of celebrities including Miranda Hart, Paul O'Grady and Barbara Windsor in the 24 Hour Panel People Challenge - designed to pay tribute to classic game shows such as The Generation Game and Blankety Blank - but was the only famous face to endure the entirety of the marathon event.
Speaking about the Comic Relief spectacular, which was broadcast live online from midday Saturday, Walliams remarked: "I'm descending into madness! It does take its toll on you just physically... it was as tough as I thought it would be, particularly at the end just having to keep the show together, being so exhausted and not being able to think straight anymore."
He added: "I just couldn't really read the autocue anymore because my eyes couldn't focus, which is quite a scary thing, especially as there was an audience here.
"It was tough, yes, but it was the right side of tough. I mean if I was slumped on the desk not saying anything, I think it really wouldn't have been very entertaining, but you could see I was a little bit delirious towards the end."
Walliams further confessed that the panel show challenge had been an even more daunting prospect than his 2006 swim across the English Channel in aid of Sport Relief.
"I trained for a long time to swim the Channel so I was kind of ready to do that. With this I had a lot less sense of how it was going to work out, because I really didn't know how I would be after staying awake for so long, and also being on TV and trying to be entertaining - it is so different."
Five 24 Hour Panel People highlight shows will be broadcast on BBC Three in the run-up to Red Nose Day on March 18.