Bipolar disorder manic or major depressive episodes can occur without an external trigger, unlike borderline personality disorder which almost always has a trigger.

“Again, in bipolar disorder, there is no need for a trigger to create a manic episode or a major depressive episode, they just happen or they can just happen. Whereas in borderline personality disorder, almost always there's an external trigger or a perception that something happened in the environment or that somebody is behaving a certain way that dramatically shifts the person with borderline personality disorder from one mode to the next.”