Britney Spears is set to judge the talent show “The X Factor” this fall, but if her behavior of late is any indication, she seems to be a nervous wreck. Could it be because she’ll be going up against her old rival Christina Aguilera?

Spears has made some headway in the past couple of years in her fight towards a comeback; after a much-maligned MTV performance following her breakdown–which had critics calling her fat and drugged–she managed to get in shape and put out a new album that garnered good reviews. However, now that she’s in the spotlight again, she seems to be a bundle of nerves. Those on the set of a shoot for her new perfume–Elizabeth Arden Fantasy Twist–say she was constantly smoking in between takes and appeared “out of it” and “robotic”.

As the date draws nearer for Britney to sit at the judge’s table on “The X Factor”, it’s possible she’s getting antsy about being in such a high-profile gig, and it probably isn’t helping that her old rival, Christina Aguilera, is judging on a similar show opposite her. Aguilera has been on “The Voice” for a while now, so she’s an old pro; it could be that Britney feels like she jumped into a job she’s not entirely ready for.

Aguilera had some kind words for her old Mickey Mouse Club buddy, however:

“I came up with Britney, we were very close,” Aguilera said. “Our paths have always crossed. They’ll continue to cross. I welcome her to this family of fun and entertainment and finding new talent. Britney’s a pro. She’s going to give great advice.”

The new season of “The X Factor” starts September 12th on Fox.