Miley Cyrus may be going back to her old, wild self.

During an appearance at this year's iHeart Music Festival in Las Vegas, the star appeared to be going back to her partying ways after giving fans a shoddy performance.

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"It was clear something was off," a source exclusively told In Touch. "Her face was so puffy and she was slurring a bit."

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Further, during her performance with Billy Idol, the singer "forgot a few verses of the song," and "seemed stoned out of her mind."

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The source revealed Miley drinks and smokes weed before her performances because it enables her to be more creative. The singer has ditched her "party girl" image since reuniting with long-time beau Liam Hemsworth, but friends and family are worried the star is back-tracking.

"She just doesn't have a stop button, which in her case, can be dangerous," the source continued.

For more on Miley Cyrus, pick up the latest issue of In Touch, on newsstands now!

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