The Spain captain injured his hand in January and, even after recovering, played no further part in his side's season.
"This has been a different experience, I have tried to recover what I had lost on a personal level," he told radio station Cadena Ser.
"Being with my [Spain] team-mates has been ideal to help me forget about the less favourable things I have experienced.
"But even forgetting not playing, we didn't win any trophies last year and I am now focused with the national team on feeling like a player again and recovering my form."
Casillas admitted that sitting on the sidelines for Madrid had not been easy.
He said: "I had a tough couple of months because I wasn't used to not playing.
"I had a lot of concerns, especially with my hand, because it wasn't an easy injury to shake off, but my doctor relaxed me and I reduced my recovery time to seven weeks and now I have no problem with my hand."
Barcelona players Xavi Hernandez and Andres Iniesta came out to support Casillas, and he was grateful for their words.
"Aside from the competition and rivalry there is a friendship that comes from spending time together and experiencing special moments with the national team. After all these years together you have to pitch in and help your team-mates," he said.
He also stressed that he is trying to learn from that unhappy experience.
"Spending such a long time without playing has made me value this sport a lot much and now I'm going to spend all week fighting to defend the goal of Real Madrid and Spain," he said.
He added that he retains a close relationship with Real Madrid president Florentino Perez and spoke to him before heading out to Brazil, and backed his decision to appoint Carlo Ancelotti as coach.
"I think it's the right move, he has won many trophies, he's won the league and the Champions League," he said.
"We are excited about doing things well again and winning trophies again. Last season was not good for us and we didn't have any luck."