"I had that life-threatening cardio vascular event back in 2007 and faced a less than 10 per cent chance of living at that time. That changed my whole outlook on life," he said.
"I had no idea what pulmonary embelism was at the time. I was just ready to get back out there and play. It really did set me back and it was a wake-up call. It showed we're not bullet proof and you can't take anything for granted in life.
"I learnt a lot about myself and that is what footy has done. It has been a great training ground for me. I said to the boys this morning it has given me a great vehicle to really learn about myself as a player, as a person and in a team environment."
Simmonds will play his last AFL game against St Kilda next week after announcing his retirement.
"I've got some things going on and and I've got a business in helping other people. I'm writing a book with a business partner that will hopefully be released at the end of the year," he said about his plans for life after footy.