The holders clinched a place in Sunday's title decider against Germany or Italy in part thanks to a Casillas save in the 4-2 penalty shootout win over Portugal on Wednesday and he said Spaniards should enjoy the moment while it lasts.
"It's strange what happens in life sometimes," the 31-year-old known as "Saint Iker" told Spanish radio station Cadena Ser.
"However badly things are going for the country in terms of the crisis and all that, football has been a kind of oasis that has allowed people to forget everything a little bit," he added.
"Football has been a source of joy and we are happy and excited about that and we want people to make the most of it as it will be difficult to repeat," added Casillas.
"These have been four exceptional years and the kids back home don't realise how lucky they are to be able to experience this," he said.
"I remember winning the gold in '92 and that was incredible so imagine what they are feeling now."
A Spanish triumph on Sunday would make Vicente del Bosque the first coach to win a treble of World Cup, European Championship and Champions League, Europe's elite club competition.
"I think this is an extraordinary group and despite the long season we have behind us they are playing with great generosity and great effort," he told Cadena Ser. "Such good players make any coach look good."
Germany play Italy in Thursday's second semi-final in Warsaw.
