Emotionally Unstable Personality Disorder (EUPD), also known as Borderline Personality Disorder (BPD), is a mental illness that severely impacts a person’s ability to regulate their emotions. This loss of emotional control can increase impulsivity, affect how a person feels about themselves, and negatively impact their relationships with others. However, not everyone who’s emotionally unstable suffers from EUPD or similar disorders. But every person who has personality disorders is likely to have unstable emotions.