Alex Trebek is sharing details about his ongoing cancer battle. The Jeopardy! host sat down for an interview with CBS Sunday Morning’s Jane Pauley, where he opened up about being diagnosed with stage-four pancreatic cancer. The show will air Sunday, but a preview was released on Thursday. 

He says that he continued to work even as he went through treatment, which led to some seriously tough days. "This got really bad. I was on the floor writhing in pain… It went from a three to an 11. And I just couldn't believe. I didn't know what was happening," Trebek tells Pauley. "And it happened three or four times a day while we were taping. So that was a little…little rough on me."

The 78-year-old said he tried to muscle through the pain: "I had 15 minutes before the next show. So I got myself together and spasms…usually last about 10 to 15 minutes. So, all right, here we go again. 'Anybody got any pain pills?' And I don't like taking pain pills. But…I got through it. And the producers were very kind. They said, 'Look, if you — If you don't want to do the show, we'll just cancel taping.' I said, 'No. We're here. We're doing the shows.'"

And his hair? Gone. But he hopes to grow it back. For now, he says he’s wearing a hair piece. 

Trebek's interview will air at 9 a.m. EST on May 12 on CBS Sunday Morning.