Dame Deborah said she had once suffered a panic attack while in the changing room of a Karen Millen store in London’s Covent Garden, causing her to flee onto the street in her underwear.
She added: “I often woke up in the middle of the night already in the grip of an episode, believing my body was dying.
“The great irony, of course, being that when I was younger and not facing death, my fear of it was so uncontrolled that quite often it stopped me from living.
“I stayed at home when I should have been out enjoying myself, I missed holidays because of my fear of flying. Do you know what finally ‘cured’ me?
“The worst happened and my fear was realised – I was told I had incurable cancer and that I would die.
“I had no choice any more – I had to look my biggest fear straight in the eye.”
In a letter to her two children also published in The Sun over the weekend, Dame Deborah encouraged them to “marry only for love”.
The podcaster was diagnosed with bowel cancer in 2016 and subsequently kept her one million Instagram followers up to date with her treatments.
Her candid posts about her progress and diagnosis, including videos of her dancing her way through treatment, won praise from the public and media alike.
In early May, she revealed she had stopped active treatment and was receiving end-of-life care at her parents’ home in Woking.
Dame Deborah co-hosted The Big C podcast
Alongside Lauren Mahon and Rachael Bland, she launched the You, Me And The Big C podcast in 2018.
The trio, who were all former or current cancer patients, candidly discussed life on treatment and other topics relating to cancer.
Bland died in September that year at the age of 40, two years after being diagnosed with breast cancer, making Mahon, 37, the only surviving original host.
As a result of her campaigning efforts, James was made a dame, with Prime Minister Boris Johnson saying: “If ever an honour was richly deserved, this is it.”
Dame Deborah later said she felt “honoured and shocked” to even be considered for the honour.
How To Live When You Could Be Dead by Deborah James is published on August 18.