On Tuesday, Carlo Ancelotti's side survived a major scare in losing 4-3 at home to Schalke in the last 16 of the UEFA Champions League, scraping through 5-4 on aggregate after their 2-0 first leg win.
It was a second successive defeat for Real, and a fifth loss since the turn of the year, in marked contrast to their 22 consecutive wins at the end of 2014.
"It's true that we've hit rock bottom quickly, but the positive is that we're in next Friday's draw [for the Champions League quarter-finals], so we can forget about the last 10 days," Casillas told Canal Plus.
"We must be united and accept the criticism from Madrid fans because we haven't matched our high standards but are now in the quarter-finals.
"We're now in a privileged position and thinking about the next game. We can't look back and remember those 22 wins or the other things we've achieved."
Casillas' display on Tuesday attracted criticism, with some feeling he was at fault for the first three of Schalke's four goals.
"I think a goalkeeper must always take the blame," he said. "It wasn't one of my best games, but it's no time to think about myself.
"Despite not having done our homework [on Schalke], we were able to progress."
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