It’s been a year since John Mulaney debuted Baby J, the comedian’s triumphant special that spun humor from his recent personal rollercoaster experiencing relapse, recovery, divorce, a new relationship, and fatherhood within a few short years. The comedian described his star-studded intervention in a particularly hilarious run—“As mad as I was when I walked in there, I was like, ‘This is a good lineup”—but in a new sit-down with David Letterman, Mulaney goes deeper on the far more serious aspects of recovering from his drug and alcohol addiction.

On the new Netflix episode of My Next Guest with David Letterman, Mulaney indulges the former Late Show host’s questions about his rehab experience. “It’s not immediately great nights of sleep and serenity,” says Mulaney, explaining that he initially had no use for anyone’s inspirational stories or encouragement. “I had zero gratitude.”

“The actual detox from drugs was very physically uncomfortable, and I’d been on a lot of benzodiazepine like Xanax and Klonopin,” Mulaney explains. “Getting off those can be very rough. I was in the detox hospital room and I was grinding my teeth so much that a molar cracked.”

The comedian had only been at the rehab for about four days but was so miserable that he told a doctor that he was leaving. “He didn’t argue or anything. He just went, ‘John, we both know how this movie ends.’ And that was it,’” says Mulaney, explaining how that line ultimately convinced him to stay. He shared that this December 20 will mark three years of sobriety for him.

During the episode, Letterman and Mulaney return to the Chicago private school where Mulaney graduated, and also sit down for a meal with the comedian's father Chip. Mulaney’s father explains what it’s like to be the inspiration behind some of his son’s best comedy material, but Letterman edges into serious territory, asking how Chip handled Mulaney’s addiction and recovery. After Chip acknowledges that he feared for Mulaney’s life, Mulaney apologizes to his father for making him so scared.

In Baby J, Mulaney admitted that the friends who staged his star-studded intervention saved his life. “Do you know what it’s like for 12 people to save your life? It’s too many people,” Mulaney said. “They could’ve done it with four people—and I know the eight they could’ve cut. Instead, for the rest of my life there are 12 separate people out there who if I’m at dinner with them I have to be like, ‘No, I got that. Come on. You saved my life. . . . ’”

When Letterman isn’t complimenting Mulaney’s material, he also asks about Mulaney’s two-year-old son, Malcolm, whom Mulaney shares with girlfriend Olivia Munn. The baby “was a big surprise,” Mulaney laughs, explaining that he hadn’t considered fatherhood much before.

“It wasn’t so much that I thought I wouldn’t as. . . it was never a good day to have [a kid],” Mulaney says. “I just wasn’t thinking about it. I was just. . . kind of living one minute to the next. And then this guy came along. I was starstruck when I met him. I went, ‘Oh, there you are.’ I was looking in not good places and then, ‘Oh, there you are.’ That was my first thought.”

If you or someone you know is struggling with addiction, you can visit samhsa.gov or reach out to SAMHSA’s National Helpline at 1-800-662-HELP (4357).