The six time gold medallist admitted he pushed himself too far last year when jumping back into “turbo training” - a high intensity interval training workout on his bike.
His wife of six years Sarra came home to find her husband on the floor in the garage and barely able to speak.
Speaking to online magazine Cyclist, he said: “‘I had been doing a turbo session in my garage. When my wife came in, I was just lying on the floor.
“I had tried to do a similar effort to the old lactate sessions I used to do as an athlete and I pushed myself too hard. It was horrible. My wife just looked at me and said, “What have you done?” I said, ‘I can’t speak!’
“Those lactate sessions were the worst,” he recalled. “I’d be in a lab on a turbo trainer and I’d do four 30-second efforts at 100% effort.
“It sounds so innocuous but the difference between 99% and 100% is huge. You can finish at 99% and you’ll be hurting but if you push a tiny bit more – and that’s the bit that makes the difference to your training – your legs just grind to a halt. It’s like your engine is seizing up.
“My coach would unclip my feet and pull my leg over the saddle so I could just slide off onto a mat and curl up in a ball.
“The real problem is that the pain actually gets worse. You have created massive acidosis in your muscles so there is a huge quantity of hydrogen ions and the pH in your blood changes. For 15 minutes you lie there thinking, ‘God, this is really bad. I’m going to die. It has never been this bad before.’
“And every time you think exactly the same thing. You have to lie to yourself by saying you’re not doing a second set. Then, without moving for 15 minutes, almost to the second, I would roll over and think, ‘OK, I think I can do a second set now’.
“During those sessions I have never felt more alive or so close to death.”
The dad-of-one, who was the first Briton in 100 years to win three gold medals at the same Olympics, also talked about the recent athlete doping scandal.
He added: ‘I’ve become Olympic champion six times and I’ve never taken a performance-enhancing drug in my life, but I was lucky in that I never even had the choice.
“I never had pressure and I never had a person come to me saying, “You should do this.
“If you are a teenage kid and are thrown into a sport or an environment where it is the norm, who knows? People say they have great strength of character but you can only talk from your experiences.”
The eleven times world champion announced his retirement from competitive cycling back in Spring 2013.
Since then he has been promoting his own brand of bikes, Hoy Bikes and earlier this year published two fictional children’s books about a young cyclist, Flying Fergus.
In 2014, Hoy’s keen interest in motorsport competitions seen him join the British GT championship and last month he debut at motorsport endurance race, the Le Mans 24 Hours.
Along with his MBE, Sir Hoy is also an ambassador for the Royal Air Force Air Cadets and UNICEF UK.