NBC posted security outside his hospital room after a man apparently pretending to be a Jesuit priest tried to enter, Leno said during the taping of Monday's show.
"So now I'm like in `The Godfather," Leno told the audience, referring to the scene in which a wounded mob boss is shielded from his attackers. "It's so stupid. But anyway, we're back and we're not gonna be canceling any more shows or appearances."
Leno is a valuable asset for NBC, which will be showcasing him in a daily prime-time show later this year after he leaves "Tonight."
The network aired reruns in place of two "Tonight" shows last week, the first time it had to cover for an ailing Leno since he took over as host in 1992.
According to an NBC transcript of Monday's show, Leno said he drove to the "Tonight" studio in Burbank last Thursday in a Model T, one of his vintage cars, on a cold morning and without a jacket.
"I was freezing and I got chills, and here at NBC we have an `ODN,' overly dramatic nurse," Leno said, who took his temperature and insisted he needed an ambulance ride to a hospital.
Instead, he walked over to nearby Providence Saint Joseph Medical Center. In less than half an hour, he said, blogs were reporting "Leno Dead!" and "NBC afraid to release story!" — which Leno called "hilarious."
Leno's spokesman said at the time that doctors found no evidence of a serious ailment. The comedian didn't specify his illness Monday.
He did milk it for punchlines, including one that played off the swine flu outbreak dominating headlines.
"What happened was — and I think was a mistake — I ate a raw pig a friend brought back from Mexico. ... It was delicious," he joked.
"And I realized I've got a really bad HMO. Like, for X-rays they had to take me over to Burbank Airport and put me through the baggage" machine, Leno said.
Conan O'Brien, who will become the new "Tonight" host in June when Leno leaves, came in for some ribbing.
At the hospital, Leno said, "I had a horrible dream that I couldn't breathe. I felt like I was suffocating ... then I woke up and realized Conan was holding a pillow over my face."
He also turned serious, thanking well-wishers for cards, phone calls and "being so kind." His "comedy stimulus tour" will continue, he said, with a free Mother's Day concert in Wilmington, Ohio.
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