Taking refuge in the mountains, the Two and a Half Men star said he ate nothing for an entire week after the 2011 split.
“I went into Big Sky in Montana, and I did no food, no drink - just water and tea," the 40-year-old told his friend Dax Shepard on his new podcast Armchair Expert.
“I took all my computers away, my phone, my everything. I was there by myself so there was no talking, and I just had a notepad and a pen and water and tea for a week.”
Kutcher said he enjoyed the extreme solitude.
“I started to hallucinate on like day two which was fantastic," he said. "It was pretty wonderful. I was doing tai chi with my own energy."
Asked about whether he had prior experience with the martial art, he laughed. “No, I was just doing what came to me," he said.
Kutcher, who described the experience as “really spiritual and kind of awesome”, said he used the experience to reflect on his past relationships and wound up writing letters to some of his exes.
“I wrote down every single relationship that I had where I felt like there was some grudge or some anything and then I wrote letters to every single person and sent the letters on day seven," he said. "I typed them all out and sent them. It was almost like an AA exercise, where I was like: ‘I probably have done some damage.' So I just cleared [my] palate.”
Kutcher, 40, and Moore, 55, got married in 2005 but split up six years later.
At the time, Kutcher released a statement, saying: “I will forever cherish the time I spent with Demi. Marriage is one of the most difficult things in the world and unfortunately, sometimes they fail.”
Moore, in a separate statement, said: “It is with great sadness and a heavy heart that I have decided to end my six-year marriage to Ashton. As a woman, a mother and a wife there are certain values and vows that I hold sacred, and it is in this spirit that I have chosen to move forward with my life.”
Kutcher is now married to fellow actor Mila Kunis - the couple have two children together.
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