Artie Lange explained his descent  back into heroin addiction on this morning’s Howard Stern Show on Sirious satellite radio.

“I fell off the heroin wagon, as we call it,” Lange said.

The tubby comic said he started snorting heroin again 7 weeks ago — but didn’t use while on a USO trip in Afghanistan.

Lange’s relapse was pre-determined, showing the man clearly has a mental problem. Lange attempted to manipulate his use of Subutex, an anti-addiction pill he calls his “night in shining armor.” Lange’s brain-damaged plan was to go off Subutex, get high on heroin, then start popping Subutex again.

Artie’s constant sleeping on the early-morning show in recent months was due to his relapse, Lange explained — in an unusually cheery interview that opened the Stern show today.

“I was probably hanging out with the wrong crowd in New Jersey. One thing led to another and I, uh, ended up getting heroin,” Lange said.

“Maybe it’s time you get new friends?” Stern joked.

In a story that first veered on a tangent about his days as a pool shark in Jersey, Artie said he hooked up with old friends from that era “who haven’t moved on in life.”

One of Lange’s old friends called him to shoot pool. Lange hesitated because of the “shady” characters involved, but apparently mosied on over nevertheless.

“I skipped the Subutex to drink,” Lange said. “I found myself at the end of the night drunk . . . Sure enough a guy, knowing my reputation, asked me if I wanted some heroin.”

(I love how Lange puts so much stock in pills)

“This guy at the pool hall, what’s his name, Satan?” Stern asked.

Lange purchased “a coupla” bags at 40 bucks a pop. He felt like killing himself the next morning due to guilt.

But he “partied on,” using heroin until just before leaving the country to go to Afghanistan. He was clean overseas, but started using again 8 hours after getting back to the U.S.

“I get back from Afghanistan, we still had a week off, you know (the trip to Afghanistan) was a success, I thought I might as well reward myself,” Lange said.

Lange’s mother and sister apparently knew almost immediately he was on drugs again.

Richard Lewis, the comic who has been sober for years, called Lange out of the blue — apparently before or right around the time Artie relapsed — and recommended he see a doctor who helped Lewis get clean.

“Look I don’t know if you have any trouble now, but this guy is unreal. He saved my life,” Lange said Lewis said.

After skipping a Springsteen concert in Jersey, Lange tried to stop.

“Everything becomes a hell,” he said, “you know, because . . ”

“You have to plan your life around it,” Stern interrupted.

“Yeah,” Lange said.

Lange was snorting at least every hour, “but it never got as insidious as coke.”

Lange said he did not take it during Stern’s morning show.

While trying to get straight in order to catch a flight to California where he was supposed to appear on the Bob Saget roast, Lange’s life fell apart.

“I ran out of heroin,” he said.

He fell asleep at about midnight and was supposed to catch an early-morning flight. He overslept, woke up in a frenzy and popped his loyal Subutex — unfortunately, with heroin still in his system, which is a big no-no.

He became ill, but still wanted to grab his written jokes and jump on the jet to Cali.

At some point he realized the drugs in his body were reacting poorly.

His solution — take multiple showers!

“You’re lucky you didn’t get cardiac arrest or something,” Stern said, after Lange indicated that his biggest problem at the time was “sweating through his clothes.”

Lange then admitted he thought he was going to die, so — he called his lawyer and left a voicemail on his cell phone.

“I was out of my mind,” Lange said.

At this point, Lange had “turned green” and he developed a splitting headache.

Lange thought he was going to be found dead in his apartment.

“Imagine if you got super powers out of all this?” Stern asked.

Lange’s lawyer called him back and Lange tried to say he had the flu and couldn’t fly. Meanwhile, he had just been writhing around his bed in pain.

Eventually, Lange’s lawyer called, with the Bob Saget roast producer on the line. Comedy Central offered to fly Lange out on a private jet with a doctor on board.

“He was going to be medi-vac(ed) to a roast?” Robin Quivers asked.

“My heart might explode on the jet . . . or I could get to the show and literally die on the show,” Lange said, adding he had promised Stern if was to die publicly, it would be on Stern’s radio show.

Lange finally threw in the towel, saying “I can’t do this. I have to get help.”

Lange checked into a rehab in Jersey, then contacted Lewis’ addiction therapist.

“Maybe I’ve hit the wall and it’s all gotta stop,” Lange said.