How long has she been medicated for? This video she looks in a trance. Also, I remember reading a story,before her dad got the conservatorship, that some guy she was dating (or was he her manager?) was giving her pills.

Britney Spears Dig

This was the reason for the conservatorship.

http://www.mtv.com/news/1580991/britney-spears-was-drugged-controlled-by-sam-lutfi-parents-allege/