Dax Shepard almost died as a teenager.

The 51-year-old actor was "seconds away" from the end of his life when he was involved in a car accident but rather than being terrified at the thought, he remembered finding the idea "shockingly comforting".

Discussing near-death experiences on his Armchair Expert podcast with co-host Monica Padman and guest Kaley Cuoco, Dax shared what had happened to him during 12th grade in high school.

He said: "I don't know what the definition is. But, I have had the moment, which is among the most unique feelings I've ever had in my life, where I went, 'Oh, I'm about to die. I'm like seconds away from dying.'

"I was in the back seat of a car. Like I had folded the seats down in the back of a Ford Probe, in like a hatchback, and my friend was driving. We were coming back from Toledo, back up to Detroit.

"It was like late at night, and I had to work super early in the morning. So I go, 'Hey, I'm gonna sleep in the back. Are you good to drive?' [He said] 'Yeah, I'm totally fine.' He had the cruise control on 85, and I'm like back there, I'm listening, and the road was really rhythmic.'

"Just at that moment, I was like, 'Oh, that rhythm's nice. I'm gonna fall asleep.'

"And then I just heard gravel hitting the side of the car. And I immediately looked up and he was completely slumped over."

Dax told how the car had been "going 85" before it "started to go sideways" and had "gone off the road".

He continued: "It's just pine trees lining that interstate in Michigan. And I started to go ... to grab the wheel and there was a moment I just knew it was too far gone. Like we had gone completely sideways.

"I laid back down and then ... we just launched in the air and we started rolling right down the highway.

"I'm like, 'We're gonna hit a tree and that's gonna be that.'

"And I definitely had this moment where I was like, 'Oh, wow, I'm gonna die in a second.' And the feeling was shockingly comforting. Like, that I remember."

The Employee of the Month actor went from feeling "complete fear" that the car was "out of control" to "very calm", which he thinks was a result of chemicals from his brain being released and leaving him feeling "kinda weirdly at total peace with it."

He added: "Then we just rolled like 10 times, ended up upside down. We did not hit a tree.

"The car was flat. We crawled out the windows … He was okay, and I was okay."

Dax is keen to share his experience with others because the aftermath saw him questioning whether or not he was still alive.

He said: "I want to talk to other folks because the trippiest part for me was post that event for about three days.

"Because I already went, 'Oh, I'm dead' and I accepted it. For the next three days, I'd just be places that I felt very peculiar like, 'Am I dead? I know I died.' That was the weirdest part of the whole thing."

As a result of the terrifying experience, Dax - who has two daughters with wife Kristen Bell - finds it impossible to sleep in a car.

He said: "It was highly memorable. This may shock you, but I've never been able to fall asleep in a car ever since. So I can never let the other person take a turn driving.

"There's no way I could sleep with someone else driving. That's a wrap on that."