The 34-year-old completed a 7.5 million pound move to Stamford Bridge towards the end of the transfer window, bringing an end to his successful spell at Villa Park.
Martinez had been linked with Juventus before Chelsea made their move, with the Blues turning to the Argentina international after doubts emerged over Robert Sanchez following the start of the season.
Sanchez has since joined Como on loan, while Martinez has taken over as Chelsea's first-choice goalkeeper.
However, the goalkeeper has now explained that his decision was also driven by a desire to put the disappointment of Argentina's World Cup final defeat behind him.
"It took a lot out of me after losing a World Cup final; the pain stayed with me for a long time," Martinez told ESPN Argentina.
"I needed a fresh start at my club to get over the heartache I felt after that final.
"I come here (international duty) and honestly feel great, happy, full of energy, and that's what matters most."
Speaking separately to TyC Sports, Martinez expanded on the impact of the defeat and his decision to seek a change.
"It took me a while to think; losing the World Cup final hurt a lot.
"I tried changing clubs to mentally refresh myself, and I succeeded. I came here (to Chelsea), and it was the best thing I did because I feel useful, fast, and good.
"In the end, I have to represent my country, my family, and I have to do my best," he concluded.
Martinez had enjoyed several successful years with Villa, helping them win the Europa League and establishing himself as one of the leading goalkeepers in world football.
He was also part of Argentina's run to two World Cup finals, but the latest campaign ended in disappointment when Spain claimed a 1-0 victory in the showpiece in the United States.
Martinez has made it clear that he is now focused on winning trophies with Chelsea, although the move has yet to bring an improvement to the club's defensive record.
The Blues have conceded more goals than any other Premier League side this season, while Martinez is still waiting for his first clean sheet.
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