Nasri was one of several City players to endure a dip in form last term, with the Premier League title slipping through their grasp as a result and Wembley heartache suffered in the FA Cup final.
Former coach Roberto Mancini paid the price for the failings with his job, but an under-performing squad acknowledge that they must shoulder much of the blame.
Nasri was among those to see his inconsistencies thrown under the spotlight, leading to 'moments of doubt' on his part.
The France international is, however, raring to go ahead of the new season and is hoping to put the troubles of his recent past firmly to one side as City begin life under Manuel Pellegrini.
Nasri told FIFA.com: "I feel good at the moment. I'm feeling more relaxed, but the last few months were very trying for me.
"Emotionally, I went through several moments of doubt and reassessment. Some of the criticism I got hurt me, and lots of bad things were said.
"I accept criticism as long as it's justified, but there were lots of lies about me. I made mistakes, I know, but I'm not the ugly duckling that some people seem to think."
Nasri concedes that City underachieved badly last term, as they ended the season empty-handed, but is confident they will bounce back stronger in 2013/14.
He added: "It was certainly a very disappointing season and losing our title of English champions was a failure that was difficult for the whole squad to swallow.
"We didn't manage to win a single trophy, and that's disappointing for a club with the standing of Manchester City. We had a very testing year but we'll learn from our mistakes to have an excellent season next year."