After hitting Rock, Smith resigned from the Academy and has been banned from appearing at any of their events (including the Oscars) for 10 years.
In his episode of My Next Guest, the King Richard star spoke to Letterman about his experiences with ayahuasca, a powerful psychedelic taken in liquid form.
Smith said that the substance had started his “spiritual journey”, after going from “never” trying drugs before to taking ayahuasca 14 times in two years.
“You’re not hallucinating,” he explained. “It’s like both realities are 100 per cent present… There’s what’s going on in your head and what’s going on in the room.
“Once you drink it, you’re gonna see yourself in a way you’ve never seen yourself.”
Smith then described one particular trip, which he called “the individual most hellish psychological experience of my life”.
“I’m drinking, I’m sitting there, and then all of a sudden, it’s like I start seeing all of my money flying away and my house is flying away and my career is gone away,” he recalled.
“I’m trying to grab for my money and my career and my whole life is getting destroyed.”
Asked by Letterman if this represented his real-life fears, Smith agreed.
“I hear a voice saying, ‘This is what the f*** it is. This is what the f*** life is.’ And I’m going, ‘Oh s***.”
Smith said that he then heard his daughter Willow crying out for help, but he couldn’t get to her. With the shaman’s help, he began to relax.
“Then slowly, I stopped caring about money. I just wanted to get to Willow,” he said. “I stopped caring about my house, I stopped caring about my career… when I came out of it, I realised that anything that happens in my life, I can handle it.”
Elsewhere in the interview, Smith said that his personal “pain” had allowed him to “reach people differently” as an actor.
My Next Guest Needs No Introduction With David Letterman is on Netflix now.