I thnk Britney is like most young celebrities.  She is still overwhelmed with papparazi, money, celebrity and sometimes it is hard to stay in control.  Also, I do believe that she is bipolar or something similar.  I have a good friend and her sister(also a good friend) is bipolar.  I have known them a long time and I have seen the maniacal ups and downs that bipolar people have to deal with.  Sister is very unstable and has been on lithium for as long as I can remember.  She gets stable for a while and starts acting 'normal' (if there is such a thing) and then goes off her meds and freaks out again.  that is a common thing with bipolarness.  They get stable and start feeling normal for a while and think that they don't need their meds.  They stop taking them and regress, not realizing that their meds are what is keeping them stable.  She is a very sweet and loving person, but when she is manic or off her meds, she is scary.   I believe that bi-polar is a medical condition that required medication and talk therapy. 

As far as her sister, she could have the same tendancies because I think that it is genetic, but not likely.