Pendleton, a two-time Olympic champion and nine-time world champion on the track, was diagnosed with severe depression last summer. She had recently returned from Mount Everest, where hypoxia had cut short her summit attempt, and her marriage to former British Cycling coach Scott Gardner had fallen apart.
After suffering a panic attack, Pendleton was prescribed a range of medication, including Prozac and sleeping pills, but she said they didn't help and only made her feel like "a zombie".
In the interview she went on to revealed the darkest moment, when she came close to ending her own life.
"It must have been about 6.30am, I had been awake for hours. I remember lying there with tears rolling down the side of my face. Not really crying but just feeling a sense of hopelessness. I was so low. So helpless. And I just thought: 'I don't want to see tomorrow,'" Pendleton said.
"I had accumulated 1½ times the dose of drugs to kill myself. And I had it there, in front of me, and I knew how much it would take. And how long I would have to be left for it definitely to work. It wasn't even like I was really upset about it. I just felt numb."
Fortunately, she made the decision to pick up the phone and call British Cycling and Team Sky psychiatrist Steve Peters, who in turn told Pendleton's brother to go over immediately. "It was the one bit of sanity in the whole process. I'm so grateful that he picked up. Because I don't think I would be here if he hadn't."
Pendleton then moved in with her mother for two months over the summer, although her mental state did not improve immediately. She revealed that she would "fantasise" about suicide, working through all the practicalities and even asking her mum to forgive her if she went through with it. "You just can't understand how much I was suffering on the inside," she said.
Pendleton now says she has "turned a corner" and is feeling much better in herself. The turning point, she explained in the Telegraph interview, was an independent trip - against the advice of family and friends - to Costa Rica, where she went surfing every day.
"Within a few minutes of being on the water I would forget about how I'd felt on dry land," she said. "There is something very healing about being on, or in the ocean. The way I felt when I came back was like: 'This is way better than any of the drugs I was prescribed.'"
Pendleton is now a patron of The Wave Project, a charity that aims to use surfing as therapy for young people going through mental health or other issues. She firmly believes that taking herself out of her comfort zone helped her start to overcome her depression and she firmly believes that sharing he experiences publicly, however daunting, can help other people.
"The truth is I don't know if I will suffer like that again. People would say 'Oh, you're looking much better.' Or 'Are you feeling better?' And I was so afraid to say yes, because I didn't know whether the next day I might wake up and feel bad again," she said.
"But I think since November I have felt much better. I've turned a corner a little bit. That doesn't mean that I won't be more cautious in the future, if I start to feel similar symptoms. But I feel I'd be better prepared at least. I guess that's why I'm speaking out now. In case my personal experience can trigger something of use and value for someone else."