Bill Clinton Was 'Delirious' with Infection in ICU, Has a Puzzle Regimen for Staying Sharp

Bill Clinton says he's feeling "fine" after a serious illness left him delirious and in intensive care for five days in October.

"I feel better than I have in two years," the former president tells PEOPLE during an interview about his video lecture series, President Bill Clinton Teaches Inclusive Leadership, which launched Thursday on MasterClass.

Clinton says his visit to the University of California, Irvine Medical Center was the result of a "longstanding infection that was essentially in hiding."

"I knew I had it 15 months ago," he tells PEOPLE. "I took a six-day antibiotic treatment. We thought it was okay, and it wasn't. So it came out, got in my bloodstream. And I was delirious for a couple of days."

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A stint in the ICU was certainly frightening for Clinton's family, including wife Hillary Clinton who visited him at the hospital during his stay, but he was initially oblivious to the seriousness of the infection.

"I didn't know enough to be scared," the former president said. "I was too sick."

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In California to conduct Clinton Foundation business in October, Clinton says he began to feel feverish and shaky but thought he could sleep it off with the help of some Ibuprofen.

"Then I woke up again, and three hours later after I'd done my first Foundation event, I started shaking again. And I said, 'This is bad, let's go.' "

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At the hospital, "they got me fixed up," the president says. "I took 30 days of antibiotics and it's gone now. And I feel better than I have in two years. I feel good."

Still, there is a lingering side effect from the fever — though it's not dangerous or even medical.

"I had two days where I think the young men who were here with me probably took notes on all the crazy things I said," Clinton says of his bout with deliriousness. "I'll probably have to live with it for the rest of my life."

HECTOR RETAMAL/getty

As for now, the former president is keeping healthy and staying sharp thanks to regularly solving puzzles and completing the daily New York Times Spelling Bee word game.

"I read many years ago that if you did a series of math problems or puzzles every day, it would cut your chances of dementia in half," Clinton says. "I get up every day and I do a couple of Sudoku puzzles and I do the spelling bee in the New York Times, which is a lot of fun."

His wife — and even their daughter, Chelsea — often joins in on the fun, the former president added. "Hillary and I practically celebrate if we get all the words and we compete with our son-in-law and daughter and our five year old grandson who, believe it or not, sometimes finds words I miss."