It's a scary time of year to be in Hollywood!

Tons of celebs stepped out for Universal Studios Hollywood's Halloween Horror Nights over the weekend. Demi Lovato brought a bunch of pals with her, including BFF Hanna Beth, as did Dancing with the Star castmates David Arquette, Ricki Lake, Kym Johnson, Chaz Bono and Cheryl Burke.

Demi had such a great time at the amusement park that she even Tweeted about it, writing, "Just thinking about how excited I am for Halloween! Went to @HorrorNights @UniStudios this weekend and it was sooooo scary - loved it!!"

Wilmer Valderama, Elijah Wood and former One Tree Hill star Chad Michael Murray also hung out with some ghastly creatures.

But David with his old co-star, Scream's Ghostface Killer? Hands down the funniest duo of the day. Sorry, Ricki!

The event runs at Universal Studios through October 31.

Ricki Lake is proving to be a real trooper after continuing with dance rehearsals despite suffering a painful injury.

The Dancing With The Stars diva, who was seen limping after twisting her ankle while practicing, still managed to keep a grin on her face. Producers for the show weren't taking any chances ... and called an ambulance.

Ricki refused to go to the hospital. Go Ricki, go Ricki!

We're told her professional partner Derek Hough was extremely concerned following the incident. What a guy!

Will Ricki's injury be included on the premiere episode? We wouldn't put it past the show's producers.

Ricki Lake is the first Dancing With The Stars contestant to suffer an injury while practicing for the hit ABC show.

Producers were forced to call an ambulance for the 42-year-old talk show host after she twisted her ankle while rehearsing with professional dancer Derek Hough.

Ricki Tweeted the above photo and the following:

"Not sure how my bruise turned into a medic showing up? I'm fine!!"

We're told Ricki refused to be taken to the hospital and remained at rehearsal.

UPDATE: Video of Ricki Lake still at practice ... coming soon!

Our photogs caught up with the just-announced cast members of Dancing With The Stars on Tuesday, and former talk show host Ricki Lake was excited to get started as she headed to the dance studios!

In a video posted to her Twitter account, Lake reveals that she is "terrified" to do the show! She says:

"I'm not a trained dancer -- I have no idea what I'm doing! I'm hoping to channel Kirstie Alley -- she was a big inspiration for me last season."

Alley sent a supportive Tweet back, saying, "@RickiLake .....Girl, Rock that party hard!!! Show em how it's done....Love, Mommy...;)"

Lake's been Tweeting like crazy since the announcement. See the pics she sent out of her and contestants Rob Kardashian, Nancy Grace and David Arquette after the jump!