Once in the ambulance, paramedics can be seen trying to strap her legs down before taking off.
We're told Britney is being taken to a local hospital on a "medical hold" -- essentially a mental evaluation. Cops found her earlier this evening at her home under the influence of an "unknown substance."
Cops were called to the popnightmare's home in Beverly Hills this evening, after she reportedly refused to return custody of her two kids to their father's bodyguard. Oh, the insanity of it all!
UPDATE: Britney has arrived at Cedars-Sinai Medical Center. We're told as she was brought out of the ambulance, she flipped off the waiting paparazzi. Oh my God. That Britney's shameless!
Keep refreshing for updates!