wow! Pinkie and I have so much in common.
Anyways, I'm no psychologist, but I basically see Pinkie's breakdown as a sign that she has a ridiculously wild imagination and is sometimes prone to overreacting ("Bats on my face!"). Pinkie is, by nature, unpredictable. Her thought processes function at an incredibly fast rate, often overshooting the matter at hand. Add this to her mangled sense of proportion, and you have a pony who can draw just about any conclusion from any situation. Medically, there is nothing wrong with her, but her insane behavior is simply a product of her unusual way of looking at things.
I honestly don't know how well I did here, but that's what I think.