Carrie Underwood says one thing about returning to ‘American Idol’ gave her ‘this flash of fear in [her] heart.

Carrie Underwood is back on American Idol after winning the show 20 years ago during season 4.

While she may be a judge this time around, that doesn’t mean she has forgotten what it’s like to be a contestant — and she revealed during Monday’s (April 21) live show that she still has “PTSD” from one aspect of the show.

In an Instagram video posted during a commercial break, Underwood confessed that “the Idol theme song gives me anxiety.

For real!”

“For the record, the American Idol ‘da da da da da da da da Baaa-errr’, the music, it like gives me anxiety.

I get like this flash of fear in my heart, like nervousness, because it’s the same! PTSD,” said Underwood with a laugh.

If you’re wondering what exact piece of music Underwood is referring to, check out this short clip of the show’s theme music.

But in all seriousness, Underwood told ET Online after her first live shows that she’s “having a blast” being back on American Idol.

“It’s a lot of fun.

More than anything, I love to just like be a fan.

I love sitting out in the audience, and there’s a song I know, and everybody’s having fun with it, it’s fun for me! I’m having a blast,” said Underwood.

But she did say it was incredibly hard to be responsible for sending six of the Top 20 home — America voted on the Top 10, and then judges Underwood, Luke Bryan and Lionel Richie chose four wildcard spots, thereby ending six contestants’ time on the show.

“It was one of those things where we try to think of what people want to see, the talent is insane and somebody’s gotta be voted off,” said Underwood, adding, “I don’t take it lightly that we have people’s futures in our hands, and I really would like just America to vote.

I don’t want to be put in that position again, so it’s up to you guys.

You have to vote for your favorites.

“