Former Marine Paul Whelan described the “torture” he endured while being held captive in a Russian prison for years. “The Russian government wanted to put pressure on the United States by treating me badly. Sleep deprivation is considered torture,” Whelan said Sunday on CBS’s “Face the Nation.” Whelan was part of a historic prisoner swap in August that also freed Wall Street Journal reporter Evan Gershkovich. Whelan was arrested in 2018 and convicted of spying, charges that he and his family deny. He was sentenced to 16 years in prison. Whelan was often skipped over when the U.S. secured past prisoner deals, including one that freed WNBA star Brittney Griner. He said the Russian prison kept a light on for 24 hours a day in his cell, which made sleeping very difficult. Guards would come to wake him up every two hours. “They’d shine a light in my face and take a picture. At first, they would ask me, you know, what my name was, things like that. But it turned into harassment,” Whelan said. Although Whelan has been back in the United States for just more than two months, he said it’s been “very, very difficult” to change his sleep patterns. Whelan said he is writing a book about his arrest and time in prison. “I think it’s important for me to share what’s happened to me and why it happened, so that others in, you know, similar lifestyles, traveling the world, working abroad, don’t fall into the same trap that I did,” he said.