Rachael Beck and Aidan Leslie
It has been known that Brittany Spears has Bipolar and Personality Disorder since 2007-2008. It seems like Brittany's mental illness was triggered by the intense amount of negative fame and not being able to handle the drugs and alcohol. She shaved her head in 2007 because "she couldn't handle the stress".
While Britney Spears has never publicly discussed her diagnosis, many psychiatrists have speculated that she suffers from bipolar disorder. This is based on the behaviors she exhibited before being placed in the care of her father -- many of which are classic symptoms of bipolar disorder. Whether she is bipolar or not has yet to be confirmed, but the speculation alone has brought much needed awareness for the disorder. People also believe that she has post partum depression, which feeds into her bipolar disorder.