The Philadelphia 76ers star joined from the Brooklyn Nets in February and averaged 21 points, 7.1 rebounds and 10.5 assists per game across 21 matches in his opening campaign.
He signed a two-year $68.6million deal in July and is ready to fight for the NBA championship this season.
Speaking about his high standards as a player, Harden said: "For the most part, I'm to myself.
"Media or whoever, they talk and shoot their little jabs and shots or whatever the case may be. And I never respond, just because I know who I am and I know what I'm about.
"But mentally, it was very, very difficult for me just because I'm in love with the game of basketball. If the money wasn't involved, I'd be playing basketball. And before the injuries, I think everybody knows that. It was very difficult.
"A lot of tough times, lot of dark moments, which I've never really went through because I was always healthy and playing the game of basketball. But I'm in a really good space and I feel like I'm back to where I needed to be, where I'm supposed to be. The feeling is great."
Harden then revealed he has lost 100 pounds over the summer as he prepares for his first full season playing in Philadelphia.
"At this point, it's dieting, it's proper rest, and then gaining more muscle mass, which I've always had," Harden added.
"It's just the last year and a half, I wasn't healthy enough to put the proper work in like I'm used to. This summer was huge for me in that aspect - the hill runs and the weightlifting, and then adding the skill on the court, as well."