Over the weekend, “Saturday Night Live” fans got to witness something as rare as Daria Morgendorffer smiling when longtime cast member Heidi Gardner broke character during a now-beloved “Beavis and Butt-Head” sketch.

Yet for Gardner, it was no laughing matter.

“I had coached myself for so many years to not break,” Gardner told Vulture in an interview published Monday.

Gardner, who has been on the show since 2017, takes pride in her ability to maintain a straight face even during the most ridiculous of scenarios, so when she left the stage after the sketch aired, she said she had a sinking feeling.

“I left the stage a little bit in shock,” the comedian said. “Then the anxiety set in and I was like, ‘Oh my God, was that okay?’ I had some friends in my dressing room, and they were like, ‘Of course, it was okay.’ So many other writers and cast members came up and said, ‘Good job.’ I’m like, ‘What? I actually didn’t do my job.’”

In the sketch, Gardner plays a reporter hosting a town hall discussion about artificial intelligence with an MIT professor (Kenan Thompson). During their very dry conversation, Thompson’s character keeps getting distracted by a man with a “blonde pompadour” sitting behind Gardner who looks exactly like the slacker Gen X cartoon character Beavis (played here by Ryan Gosling) from MTV’s “Beavis and Butt-Head.”

After a while, Gardner asks the Beavis lookalike to move, since his mere presence is derailing their serious conversation. He moves and Thompson’s character gets back on topic. But when the camera pans back to Gardner, there’s now a man who looks exactly like Beavis’ best friend, Butt-Head (played by Mikey Day) sitting right behind her — complete with a “gray shirt and exposed gums.”

Gardner’s character, who is now completely exasperated by all the hiccups in their chat, then turns to the Butt-Head doppelganger to ask him to move — but when she looks at him, Gardner completely loses it.

The “Shrinking” actor told Vulture that although she giggled a bit at Day’s Butt-Head during the dress rehearsal earlier in the day, something about seeing him in that moment just tickled her funny bone.

“Mikey does seem to turn his head just a little bit and bug out his eyes,” Gardner said of the moment. “It’s like he’s doing a subtle acknowledgment. That was new.”

“Mikey and I sit next to each other during table reads, and he makes me laugh a lot,” she added. “It’s easy for us to mess with each other. Something in the way he moved on live television felt like when someone messes with you to make you laugh.”

Gardner expressed surprise that “all the feedback I’ve gotten since” the skit aired suggested that “people were okay” with her breaking.

“Not only okay with it, but encouraged it,” she told Vulture.

But Gardner also explained why it was “really hard” for her “to give myself any sort of credit” for breaking character.

She told the entertainment website that when she began her career in comedy at the Groundlings, she was once reprimanded for breaking character onstage on a regular basis.

“We got a stern talking-to, and I understood why,” Gardner said. “I decided after that, I need to be professional. That cured my breaking, which happened before I got to ‘SNL.’ It had been coached into me that I couldn’t break, so I just didn’t, really, after that.”

Still, she admited that her reaction to Day had one silver lining.

“Being a perpetual people-pleaser rule-follower, it was nice that I broke the rules — unintentionally, of course,” she said.