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The world number six, who beat Barry Hawkins 10-1 in Sunday's final, said: "I've taken up smoking again, just because of this tournament.
"I've been getting lazy. I've been eating like a pig and haven't run for two weeks."
O'Sullivan, the five-time world champion, jointly holds the record for most Masters wins with Stephen Hendry.
He also equalled the biggest-ever margin of victory in a Masters final, tying the 9-0 win Steve Davis enjoyed over Mike Hallett in 1988.
O'Sullivan only returned to action in mid-December after around eight months away from the game.
The 40-year-old said his performance during his semi-final win over Stuart Bingham left him feeling "embarrassed".
He also wondered if he was playing poorly because of a bad back he was suffering from or some other reason.
"I was just concentrating on trying to contain my emotions," said the Englishman. "I was pleased I was able to hold it together."
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O'Sullivan, who made breaks of 136 and 82 as he swept to victory, attributed his win to his ability to modify his game in order to remain competitive.
"I've tried to reinvent myself," he said. "I've looked at a lot of the younger players coming through - Neil Robertson, Judd Trump, Ding Junhui - and they're just such great potters and great cueists and power players.
"I decided that if I was going to challenge these players, I'd have to change my game slightly, to try and add a bit more power to it.
"So when you get on the black you can open the balls up and try and win the frame in one visit.
"I think that's helped. The game does move on and you've got to move with it."
O'Sullivan, who will seek a sixth World Championship title in April, said winning the Masters despite struggling with injury would boost his self-belief.
"It gives you massive confidence," he said. "It just shows that I don't have to be on my best game, as long as I'm mentally on the ball and giving every shot every care it deserves.
"You can play your way into form sometimes. I got a bit lucky this week. I relaxed into the game and in spells I played all right."
He added that it was "unbelievable" to equal Hendry's record, adding: "It's been a good start to the year."
Ronnie O'Sullivan says he was "stressed" by the pursuit of his sixth Masters title.