I just want to point out that the ponies under Discord's spell were not aware that they were under a reverie. When Rainbow Dash is brought back to her normal self, she asks what happened to her. She has no memory of what she had done in her Discorded state. Thus, ponies were not necessarily miserable, but their personalities were possessed with a predetermined personality that Discord force-manipulated into them. None of the mane six had latent bad personality traits that could be manipulated. Pinkie Pie doesn't have latent anti-social abilities. Yes, she became anti-social once in the show, when she believed that she didn't have her friends anymore, but as you know, Pinkie's whole life is making people happy and being a good friend. So, my argument is that the ponies never had those personality traits to begin with and that they were manipulated into their minds by Discord. Basically think of their bodies being possessed with an alternate being that is opposite of them in nature. And also, when someone is possessed, they have no memory of ever being possessed.