What is it called when one adopts a different personality(?) after some sort of an event?

If your talking about having different social personality then its called a alter ego. This is when someone having a different personality than the one they usually demonstrate. Or if your talking about a mental disorder then its called bipolar disorder. With bipolar disorder one experience manic and depressed moments. They can be super happy at one moment and extremely sad the next. Bipolar is a treatable condition but not curable.