What is Bipolar disorder?

Bipolar disorder is a mental illness that manifests itself in a person through ups and downs in moods and energy levels. Many a time, it is confused with depression and sporadic mood swings. However, it must be understood that bipolar disorder is not a state of mind. It is a brain disorder - a mental illness which is long term. Till now, no permanent cure has been found for the same. What is it all about then