Margaret Cho swears she wasn’t high during her onstage meltdown last week, so what led to the comedienne’s troubled night?

A source tells Page Six that while Cho, 47, was “phenomenal” during her previous performances at the Stress Factory in New Brunswick, NJ, this weekend, something seemed to have happened between the 7:30 p.m. and 9:45 p.m. shows Saturday night.

“Whatever happened, it happened between shows,” the source said. “Every show before that was great — she got a standing ovation for every performance and was hilarious and sharp. But for the Saturday late show, she was really incoherent, slurring into the mic and needed help just to walk onto the stage. She had to lean against the back wall to keep from falling over.”

Cho reportedly caused two-thirds of her sold-out crowd to walk out, and our source added that a doctor who was in the audience only stayed for the show’s duration because he was concerned that the comic might need medical attention.

It’s unclear whether Cho was under the influence of any substances, as sources close to the comic insisted they didn’t see her use anything or even drink throughout the weekend. But a September 2015 Billboard profile of Cho noted the presence of medical marijuana and paraphernalia in her home.

Cho has opened herself up in the past about her struggles with substance abuse, dedicating the lion’s share of her 1999 book and off-Broadway show, “I Am the One That I Want,” to her drug, alcohol and body image issues, as well as talking for the first time about her history of sexual abuse.

Cho discussed her abuse with Billboard, explaining that it was ongoing for years as a child from ages 5 to 12, then again as a teen. “I had a very long-term relationship with this abuser … I endured it so many times, especially because I was alone a lot,” she explained.

A different acquaintance sexually assaulted Cho starting at age 14. “I was raped continuously through my teenage years, and I didn’t know how to stop it … For me, I think I had been sexually abused so much in my life that it was hard for me to let go of anger, forgive or understand what happened.”

Cho began to undergo therapy at age 27, which inspired some of her comedy and led her to try songwriting. Her musical career expanded other horizons, too: Cho divorced her husband of 11 years, Al Ridenour, with whom she had an open marriage. “I’m not polyamorous anymore. But I was in my marriage, and it was great. It opened me up to a lot of things sexually, but I just don’t think it’s my style.”

Her current style? Musical partner and fiancé Andy Moraga, who accompanies Cho’s vocals for their band Dog Children on songs like the aptly titled “I Want to Kill My Rapist.” The lyrics to that particular tune include lines like, “I want to kill my rapist, I want to kill my rapist.”

It appears Cho was referencing at least part of the tune when her Saturday night performance began to fall apart.

“A lot of what she was saying was her actual standup material, but she kept forgetting the punchlines, so she just repeated [herself] over and over again … Then when she started to tell the same story for the third time in 15 minutes (maybe even less), people had enough and started to leave. The setup to the joke she was trying to tell was ‘rape is bad, kill your rapist.’ It sounded to an unknowing audience that she was just chanting that rape is bad, and then she started screaming ‘kill your rapist’ over and over again,” an audience member previously told Page Six.

Perhaps Cho’s meltdown, which she has written off as “a bad day at work,” was simply a misguided attempt at mutual catharsis for the comic and her audience, which she says is as much of a goal as laughter during her performances.

“Standup comedy is a very difficult art form, because it’s the only one that demands a physical reaction from your audience not just from the work itself, but every 10 seconds at least. [I’m] trying to use my pain to heal others,” Cho told the Village Voice earlier this month. “That’s all I have — is the knowledge of my own suffering. So then I can amplify that and hopefully make it somewhat entertaining, so that other people who feel the same way feel free.”

And if you don’t feel the same way? Stress Factory owner Vinnie Brand will gladly issue you a refund.