"The World Cup wasn't really like that for me, it was a duty to my country," he said. "There was too much on the line. There's too much at stake. I was a senior member of that team and it was a job I just had to get done and then move on with my life.
"Even to my teammates, I knew I couldn't show any weakness. I didn't sleep very well, I was pretty much rundown by the time we reached the final," he said.
"The pool stage was fine but when we reached the quarter-finals I shut myself down, it was business time. I was in tears after the whistle in the final and that was because I had put so much pressure on myself."
He said playing for Fukuoka in Japan, Leinster in Ireland, and Leicester in England since the World Cup were a way of winding down from winning the Webb Ellis Trophy.
"I've done my causes, since then I've had fun."
Thorn, who struggled to adapt to rugby at the start when he joined the Crusaders as a No8 from the Broncos, then went on to be a powerhouse lock, a fearsome scrummager and good lineout operator in set pieces not applicable to the 13-man game.
"My goal was to play top-level rugby at 40 and to play well, and I've done that," he told the BBC.
"I've been part of all these teams and it's been awesome but I just think maybe I should do something else."
Thorn, who will settle with his wife and four children in Brisbane after his time in Leicester, wants to maintain his famous fitness into old age.
He said he loved the physicality of rugby, but he main thing he would miss was the camaraderie.