Pendleton (who won gold and silver medals at the 2012 London Olympics) was supposed to attempt the summit of the legendary peak with her friend Ben Fogle for a new documentary, but had her time unexpectedly cut short when she was struck down by both mental and physical ailments.
“I’ve been suffering with depression since I got back from Everest,” Pendleton tells Radio Times in a new interview. “I feel psychologically and physiologically damaged.
“It’s really put me through the wringer, and that has been harder than any disappointment about not making it up to the summit. It’s like I’ve taken a real battering. I’ve never felt so overwhelmed with illness.”
In the interview, Pendleton explains that doctors have now told her that the depression was triggered by hypoxia, a condition that struck her due to her body being deprived of oxygen when she was over 21,000ft on Everest.
“But I felt even further away from myself then,” she confesses.
“They’ve assured me that it’s quite a normal thing and in time it will pass.”
Recalling the symptoms, she describes them as “a horrific headache, like knitting needles sticking in the back of my skull.”
“You act like you’re very marginally drunk,” she adds. “It’s not unpleasant, you’re not totally suffering, but signs of the onset of a cerebral edema [swelling of the brain caused by excess fluid] are very subtle.”
Now, though, Pendleton (who has spoken openly about other mental health issues in the past) feels less overwhelmed by her unsuccessful Everest climb, having come to accept that failure “wasn’t about my commitment, focus or fitness, but my physiology and genetics.”
“Everest is not a mountain to be trifled with,” she says. “She’ll decide if you’re going to make it or not.”
You can read the full interview with Victoria Pendleton in the latest issue of Radio Times magazine, on sale from Tuesday 26th June
The Challenge: Everest airs on Saturday 30th June on CNN
Sign up to the Radio Times newsletter for the latest TV and entertainment news