Borderline Personality Disorder (BPD), or Emotionally Unstable Personality Disorder (EUPD), can cause you to experience rapid changes in emotion. This is often triggered by your relationships. Personality disorders may effect how a person thinks, feels, behaves or relates to other people. A personality disorder often occours due to someone's life experiences, which in turn causes tehem significant difficulties. It's important to note that someone with a personality disorder does not have a "wrong" or "bad" personality.