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The world champion made a bad start, ran off the road on the first lap and later damaged his car in a collision with Red Bull's Daniel Ricciardo.
Hamilton said: "I was all over the place. I really don't have any words to describe what happened. It was a really bad performance from me.
Ferrari's Sebastian Vettel won ahead of Red Bull's Daniil Kvyat and Ricciardo.
Running fourth on the first lap after a bad start, Hamilton ran wide at the chicane, dropping to 10th place, fought back up to fourth place and then broke his front wing colliding with Ricciardo after a restart following a safety car period.
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Vettel eventually sealed victory after taking the lead from Hamilton off the start line.
That led to a pit stop and a drop down to 12th place with 20 laps to go, from which he fought back to finish sixth.
Hamilton added: "I don't know if it was a lack of concentration or what.
"I pushed right to the end but there were so many obstacles. It's like there were two different directions and each time I chose the wrong one."
He admitted it was "bizarre" that in the circumstances he had extended his championship lead over Mercedes team-mate Nico Rosberg.
The German finished eighth after a late-race collision, while fighting for second place with Ricciardo, caused a puncture and a stop for fresh tyres.
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The incident was reviewed by race officials and Rosberg said they had decided to take no action.
"Do I deserve any points?" Hamilton said. "By the grace of God I got some points.
"I have to go away from this, take breather and come back in Spa [the next race on 23 August].
"To come away knowing this was one of the worst performances I've put in for a long, long time… I don't generally try to rely on luck. The team have worked incredibly hard. The race was a bit wobbly."
Rosberg, who had been on course to make up a hatful of points on Hamilton until his crash with Ricciardo, admitted it was a lost opportunity.
"A very disappointing day," he said. "It is the sort of day I need to make the most of it against Lewis and it didn't work out.
"I just snagged Daniel's front wing on the exit of the corner. I trust the FIA and they have decided to take no action."
"[I need to] just keep going. It was close. This is half time [in the season] but with tiny differences I could have had the lead at half-time.
"Could, should, would, whatever. I have a good chance to pass Lewis in the championship at some point soon."
Full race results
Lewis Hamilton accepted the blame for the errors that led to him finishing sixth in Sunday's Hungarian Grand Prix.