The former The Only Way Is Essex star – who has previously battled weight issues and a cocaine addiction that led to two overdoses – was a contestant on the latest series of the Channel 4 reality show.
When it was announced he had signed up, the star said the series – which sees celebs going through tough military training exercises – “pushes you to breaking point”.
And he’s now told The Sun: "I remember just having a breakdown when I come out.
"I remember it was just a relief, that I was out, and it was a feeling I had for a good 24 hours that I felt it was crazy. It all felt a bit mad."
But Argent, whose nickname has long been "Arg", said that afterwards he realised how “proud” he was of himself and how much perspective the experience had given him.
"I went in as Arg and came out as James," he said.
The star, 35, said now when he introduces himself to people he is no longer Arg from TOWIE but James, who has a career as a wedding singer.
Argent has been open about his health struggles but has turned his life around in the last few years.
He is now sober and shed 14 stone following a gastric sleeve operation.
Speaking on The Cabin Recovery podcast last month, he said that his health was now "number one" priority.
Other celebs taking part in the latest series of Celeb SAS include Matt Hancock, Danielle Lloyd, Michelle Heaton and Gareth Gates.
Celebrity SAS: Who Dares Wins is on Channel 4 on Sundays at 9pm.
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Watch: James Argent "proud" he overcame his addiction issues and shed 14 stone