The Welsh rugby star claimed that the task where he was asked to swim underwater in an icy ford left him fearing for his life.
"The toughest challenge I did was probably having to swim under ice. It was mindblowing. I still think about that now," he told DS.
"It was tough. Just wait until you see it. It was wild. I'll be honest about it, I do have nightmares about it. It was frightening, but I'm glad I did it."
Henson also admitted that he "got very competitive" during the reality show and confessed to having a few rows with his co-stars "along the way". "But it was nothing personal," he added.
71 Degrees North starts on Saturday at 9pm on ITV1.
> Click here for our full interview with Gavin Henson