The 45-year-old from Rockbridge Baths, Va., made the announcement Wednesday during the Lowe's Motor Speedway media tour.
One of stock car racing's most popular drivers, Mast's career highlight was winning the pole for the Inaugural Brickyard 400 at the Indianapolis Motor Speedway in 1994. He failed to record a victory in 364 Winston Cup starts.
Mast said the symptoms he suffered were comparable to the "worst hangover of your life."
"You wake up feeling nauseated and you want to throw up and you can't," he said. "Your head is pounding all the time and you just feel awful. That is what I lived with for 5 1/2 weeks, seven days a week."
Mast said he lost 43 pounds and made numerous trips to a variety of doctors before it was determined he was suffering from carbon monoxide poisoning. Doctors are unsure when the poisoning will be completely out of his system. Sometimes it takes up to a year.
"I cut grass one day in June and the air was blowing just a certain way and the fumes were blowing and I was down for five days after it," Mast said. "I was a grease monkey of sorts. In the winter time, we worked in the garage with the doors shut and the windows closed and all the cars running."
According to Gary Nelson, NASCAR managing director of competition, the sanctioning body is investigating the problem of carbon monoxide poisoning at its Research and Development Facility in Concord, N.C. The $100 million facility was unveiled Tuesday.
Air filter systems are being tested and evaluated for possible use in race cars.
"What we're looking for is a way to get drivers to breathe the freshest air possible in the car," Nelson said. "The way to do that is to find a way to bring air from the outside through a hose into the helmet."
Even Winston Cup champion Tony Stewart suffered effects of carbon monoxide poisoning during his run at the title.
"I have been pleasantly surprised with the way NASCAR has handled this and attacked this," Mast said. "From the moment I told (NASCAR president) Mike Helton, they have taken this thing and run with it in trying to get data on it and solve this problem."
Mast's best career Winston Cup finish came at North Carolina Speedway in October 1994, when he placed second to Dale Earnhardt in the ACDelco 500. He ended his career with 36 top-10 finishes and seven top-fives.
Mast won four career poles, most recently for car owner Butch Mock in the 1998 GM Goodwrench Service Plus 400 at North Carolina Speedway. His first came with car owner Richard Jackson in his 93rd career start at the 1992 Hooters 500.