Cohen has had minor episodes over the year, but was cleared to compete at the worlds.
He has described the feeling as "once you're into the race, your heart isn't in rhythm, oxygen is running out and you lose power and become weaker and weaker as the race goes on. It feels like you're dragging something behind the boat".
Yesterday, Cohen acknowledged the significance of his decision.
"It was not a decision I took lightly but I know it's the right time," Cohen said. "I have thought about it very hard over the past few months and I feel I have achieved everything that I wanted to achieve in the sport."
His Olympic gold was part of a terrific performance from New Zealand on the Eton Dorney course.
There were other golds for single sculler Mahe Drysdale and coxless pair Eric Murray and Hamish Bond in London. However, the most exhilarating of the winning performances came from the double scullers.
Where Murray and Bond demonstrated their four-year-long superiority in their discipline by streeting their field, and Drysdale got his nose in front and stayed there, Cohen and Sullivan got home with a late surge.
The pair had developed a habit of coming home on a wet sail over the final 500m of their major races. So it was in London.
They didn't doubt they had it under control once their boat started to move through the field. They knew their capabilities, knew they had timed their run just right.
It was a remarkable achievement and things seemed set for the pair to defend their crown in Rio in 2016.
Cohen had long been an achiever at top level. He won silver medals twice at the world junior champs in 2003 and 2004, and again at the under-23 championships in 2005, and was the country's first gold medallist at a world university games in 2006.
In 2008, he teamed with Rob Waddell to finish fourth in the double scull in Beijing. That was the stepping stone to London.
Cohen has taken a banking job in Cambridge.
He'll have a pile of memories and a record of which he can be immensely proud.
