Diagnosis of this disorder is very chancy. You see, there are two disorders that often present with similar symptoms. There's another disorder, rare enough that it doesn't really have a name. In this disorder, people lack the normal filters that mediate emotions. They feel emotions at 100%. When they hurt they hurt completely. When they feel it's the end of the world, for them it really is. Some of the symptoms of this disorder that are unlike HPD are that these people are also very sensitive to light, to loud chaotic noise, overly sensitive to crowds of people. They have a hard time dealing with any kind of chaos and disorder, and don't adapt easily to change.
One thing to remember about HPD is that the people who suffer from it genuinely believe that things really are as bad as they express them. They really are hurting as badly as they say they are, but it's a self imposed over reaction to the situation causing the pain. They're not actually aware of what they're doing. They really do believe the world actually does center around them and they deserve to get the things they want. As life goes on and they don't get what they want, the disorder grows more severe.
There's really no good way to deal with it, truthfully. Though anti-anxiety drugs can sometimes help.
