Nasri struggled to find any consistency for City last term and as a result his confidence dipped.
Rather than discuss his increasing self-doubt, the France international chose to keep it to himself, and acknowledges this affected his form for both club and country.
The 26-year-old only scored two Premier League goals in 28 appearances, and found himself dropped from the France squad after a disappointing European Championships.
"I wasn't feeling myself. It was a tough season," he admitted ahead of City's UEFA Champions League clash with Viktoria Plzen.
"It was a little difficult. In my head, I wasn't the same. I didn't play well for City and lost my spot in the squad and, at the end of the year, you look at your season and you realise, 'I was not myself'."
"I didn't want to talk or explain myself. I didn't want to talk about the situation because it was really difficult and it was inside me.
"So you spend all the time thinking. Sometimes when you do mistakes, you don't want to admit it. That was my biggest mistake. Keeping things to yourself is never good.
"So I talked to the people I love and I decided to smile and be happy and do what I do best - playing football, and that is it.
"As a player, as a person, I grew up a lot. I know my mistakes now, and I know what to do to make it right."
The arrival of new manager Manuel Pellegrini has lifted Nasri's performance levels and the midfielder has already matched last season's goal tally in just 12 appearances.
