The Irish actor, writer and comedian created the HBO series, which debuted in 2016. It starred Sarah Jessica Parker and Thomas Haden Church as a middle-aged couple going through divorce.
Appearing on Desert Island Discs, the Catastrophe star explained that spending five months in Brooklyn, New York was difficult because it kept her apart from her then-husband, Jeremy Rainbird, and her two daughters.
“I lost my mind completely and I got OCD from it. I developed anxiety,” she said.
“I would lie in bed at night and I would feel my heart going and I would think: 'Oh, I am about to have a heart attack'. It was only afterwards that I realised it was anxiety.”
She continued: “I didn't not see my kids for five months. Every couple of weeks I would go back or they would come over. But it was still ridiculously long and painful.”
When Horgan met with her family for Christmas in Austin, Texas, she broke her ankle jumping on a trampoline and struggled with her injury upon returning to the set.
“It was terrible,” she said. “I went back on set and I was an even more annoying presence because I would be walking up to people on crutches giving them notes.”
Horgan and Rainbird divorced last year after 14 years of marriage.
She told host Lauren Laverne that co-parenting filled her with doubt as to whether she was a good mother.
“I was fun mum for years,” she said. I entirely thought that was my role but that changes when you co-parent.
“Everything changes and you take on a lot more roles and I am much more practical than I was, and I think that is a positive thing."
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She continued: “It had some dips in the middle where I thought, 'Oh, that thing I thought I was, which was a good mother, I am not entirely sure about'.
“When you bring anything like that into your kid's life it's tricky, when you turn the roles upside down, but it balances out and everything eased back.”
Horgan’s music choices on the show included David Bowie's Rock 'N' Roll Suicide, The Smiths' The Queen is Dead, and Kate Bush's Moments Of Pleasure.
She chose Ernest Hemingway’s The Sun Also Rises as her book.
Desert Island Discs airs on BBC Sounds and BBC Radio 4 on Sunday at 11am.
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