There are sudden and dramatic shifts in self-image, characterized by shifting goals, values and vocational aspirations. There may be sudden changes in opinions and plans about career, sexual identity, values and types of friends. These individuals may suddenly change from the role of a needy supplicant for help to a righteous avenger of past mistreatment. Although they usually have a self-image that is based on being bad or evil, individuals with borderline personality disorder may at times have feelings that they do not exist at all. Such experiences usually occur in situations in which the individual feels a lack of a meaningful relationship, nurturing and support.I don't thinks Psych Central means that a BPD sufferer's entire outward persona will completely shift from minute to minute or day to day (although some mood swings can be like that). Rather, it's more along the lines of someone "searching for identity" the way a high-schooler would. One would can have certain career goals in mind and have a certain type of fashion for some months or some years. Then some stressful triggering event can cause this person to immediately switch all of this around so that the clothing choices and career goal will be completely different. Those who do not have BPD can also sometimes make sudden changes. However, those with BPD often make sudden changes in manner that those around them finding more jarring and confusing.
A helpful article on this subject is found here.
As recovered Borderline Rachel Reiland has pointed out, sometimes this identity confusion can manifest in the BPD sufferer wearing a sort of mask, trying to always appear confident and friendly to mask a gnawing self-doubt and extreme predisposition to being bothered by what other people say.
Someone suffering from BPD identity disturbances will not have an integrated, consistent personality, but instead have a highly fragmented personality, switching back and forth. The true self will emerge when one feels safe. However, once one feels threatened in some way, the impervious false self emerges as a form of "protection." Sadly, this "confident" false self happens to wall off the person from true emotional bonds, thus becoming a maladaptive obstacle to finding true lasting happiness. :'-(
Some psychologists can mistake this phenomenon for Multiple Personality Disorder. However, there is an important difference. When someone with Multiple Personalities switches from one personality to another, the switch is unconscious; the person doesn't know it is happening. By contrast, the Borderline with a disturbed, "fragmented" personality does have some conscious awareness of when she or he is changing personalities as the result of some emotional trigger. Again, Rachel Reiland explains that.
The identity confusion can even come in the form of changes in perceived sexual orientation.
But you are not cursed to permanently suffer with this. A return to psychiatric care can be of enormous help with the proper diagnosis and committed mental health professionals. Please take your happiness very seriously. :'-)