The 2008 world champion will line up in 12th place on the Monza grid for Mercedes, the lowest he has qualified since 2010 - not including last year's Spanish Grand Prix where a penalty took him from first to last.
"It was generally a really poor qualifying session," said Hamilton. "I didn't put one single lap together in Q2.
"I just drove like an idiot. That is the worst I have driven for a long, long time. I am sorry for the team."
The stewards are investigating Force India driver Sutil for blocking Hamilton's final lap at the Parabolica.
But though Hamilton acknowledged that he had been impeding, he did not think it was the primary factor in his disappointing performance.
"It doesn't matter anyway," he said of the Sutil incident. "I should have done it on the lap before anyway."
Mercedes team principal Ross Brawn told reporters Hamilton was being overly hard on himself, explaining that the driver had not realised the car had a damaged floor after hitting a kerb earlier.
"Lewis was looking OK and unfortunately caught a kerb and damaged the car underneath, and broke the floor," Brawn explained. "We didn't realise the consequences of that until a bit later in the session. It was not repairable.
"Lewis is often his own hardest critic. It's quite endearing that he's willing to make that sort of statement," said the Briton.
Hamilton comes into the Italian Grand Prix 58 points behind championship leader Sebastian Vettel.