In her first televised interview since her August release, Laura Ling said Tuesday on "The Oprah Winfrey Show" that she was told the worst could happen if she didn't confess.
Ling said she drew suspicion because she worked for San Francisco-based Current TV, a media venture founded by former Vice President Al Gore.
"I knew that that was the confession they wanted to hear and I was told if you confess there may be forgiveness and if you're not frank, if you don't confess then the worst could happen," Ling said.
"It was the most difficult decision to have to do that. I didn't know if I was sealing my fate," she said. "But I just had to trust that this was the right thing to do."
Ling and journalist Euna Lee were captured at the North Korea-China border in March 2009 while reporting about North Korean women who were forced into the sex trade or arranged marriages when they defected to China.
They spent the first few days of their captivity in a five-by-six foot jail cell.
"There were no bars so you couldn't see out. And if they closed those slats, it just went completely dark," Ling said.
The women were moved to a Pyongyang guesthouse soon after, where Ling said conditions improved but there were no showers and the power and water went out several times a day.
"I developed a system to wash where they would allow me to heat a kettle of water," she said. "I would mix it with some cold water and then I would scrub down and just splash it on me."
The women were convicted of illegal entry and "hostile acts" and sentenced to 12 years of hard labor. Ling said she was petrified and tried to prepare herself for a long sentence, "but once I heard those words '12 years' come from the judge I could barely stand up right."
She said she spiraled into a deep depression, refused her meals and huddled in a dark corner of her room. She said she sought strength by thinking about other innocent people imprisoned.
"If these people are undergoing this then I can try to muster up the strength to get through it," she said.
Ling also said she was angry with herself and would slap and hit herself as punishment for putting her family through the ordeal.
The women were pardoned in early August after a landmark trip to Pyongyang by former President Bill Clinton.