Ongur says early psychological trauma is one of the most common underlying causes of the disorder.
"When people describe these things, it is certainly often associated with a severe history of child abuse," he says. "This was one way for them to cope."
And, as in Walker's case, psychological treatment involves unifying the alters into a single personality -- allowing those who suffer from the condition to regain full control over their lives.
"The task is to get this person feeling whole again," Ongur says.
If there is a success story among psychological conditions once considered spurious, it is that of Social Anxiety Disorder (SAD), psychological experts say.
"The whole issue of social phobias was once considered something that was not very important," Kupfer says. "As we discovered, this can cause a tremendous amount of impairment, and there are a whole lot of issues developmentally which affected coping with it."
In labeling this as a disorder, he says, medical professionals have been able to help millions of people who otherwise would have been told that they were simply shy.
Ongur agrees. "It's familiar to people because it's shyness, but it's really extreme shyness," he says. "It is something that can be very real and very impairing."
Those who suffer from SAD often find themselves faced with seemingly insurmountable anxiety when it comes to interacting in certain social situations. Most common are feelings of being watched, scrutinized and criticized by others. So intense is this anxiety that it can sometimes lead to a panic attack.
In most cases, these fears are unreasonable. Counseling can often help those who live in near-constant fear of being embarrassed or humiliated in front of others. Coaching in social skills may also be needed in order to help those with SAD better integrate themselves into comfortable social circles.
"Social phobia ... is a relatively new diagnosis," Galynker says. "Many people have difficulty socializing, of course. This is just a label to help treat people who have it."
And Galynker says the changing perception of SAD and psychological conditions like it will hopefully help remove the stigma so often associated with such disorders.
"Everybody has a problem, really," he says. "Nobody does not have some sort of diagnosis."
Katie Escherich contributed to this story