The 33-year-old, who boasts 158 caps, was dropped by La Roja coach Vicente Del Bosque for Sunday's win over Luxembourg, having made a costly error in the shock loss to Slovakia four days earlier.
However, the World Cup and European Championship winner has not given up on reclaiming the number one jersey from Manchester United gloveman David De Gea.
"I'm not immortal," Casillas said. "I won't last forever but, at the moment, I feel good and believe I can help my country qualify for the Euros.
"After you fail to win a game, all sorts of things go through your mind; you feel angry. It's like when you have an argument with your brother and you think "I'll kill him", but you don't mean it. I want to keep playing for the national team for as long as possible while the gaffer wants me."
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He added: "When you've been in the Real Madrid and Spain team for as long as I have, people demand you be the best, the same player as always," he mused. "You have to live with that pressure and respond to criticism on the pitch. I savour trophies more these days."