Kelly Osbourne may have epilepsy.
The 'Fashion Police' host - who was rushed to Cedars Sinai hospital in Los Angeles after suffering a 30 second seizure on the set of the E! series - has been warned by doctors that the dramatic health scare could be much more serious than they initially suspected.
A source told gossip website TMZ.com that Kelly's medical team are running tests and she will remain in hospital for at least a few more days while they try to determine what caused the sudden seizure.
The insider said she is currently on anti-seizure medication and doctors are closely monitoring her as they believe the seizure was extremely serious.
The 28-year-old star took to her Twitter account to show her appreciation for all the "beautiful well wishes" she received following the frightening incident.
Kelly posted a picture of herself in hospital and wrote: "Thank U all 4 UR beautiful well wishes yes I did have a seizure they are just trying to figure out why? (sic)"
A medical emergency worker who was in the audience rushed to help her, and she was later shielded with blankets as she was stretchered into the ambulance.
Kelly - the daughter of Black Sabbath rocker Ozzy Osbourne and TV presenter Sharon Osbourne - is said to have turned to her co-host to say she didn't feel well before falling out of her chair shaking.
Sharon also expressed her gratitude to well wishers on Twitter, writing: "I want to thank everyone for their concern about @MissKellyO. She's doing fine she's at Cedars and is surrounded by the best doctors & love."
- BANG! Showbiz