Disorders are problems of the mind. Disorders can be caused in both nature and nurture.
If someone loses their hand during working around heavy machinery, is it anymore gone than someone that cuts their hand off to be cool?
Plus, disorders are really more of a description of how the mind works. Any human being has a mental disorder that can be categorized based on their symptoms. It just usually isn't unhealthy. As well as the fact that people used to never talk about disorders, and problems they felt they had. Humanity has always been like this. Now, people talk about it. Before, only the severest and most dangerous cases got attention, because it couldn't be hidden. Besides, even if it isn't severe, if there are medications to help it, why not take them? Air conditioning isn't actually necessary, but it makes life a lot easier.
Aside from that, since it's about mental disorders, and not what causes them and if they're real, I'm not sure what I have. I've seen multiple mental health professionals, and gotten a variety of disorders suggested. Post-traumatic stress disorder, borderline personality disorder, depression, social anxiety disorder, social phobia and avoidant personality disorder. These are the ones I remember being mentioned.
I think I'm mostly over my PTSD, if I even have it.. .-.
But yea, that's about it. I think synesthesia would be pretty cool to have, honestly. Too bad all the aforementioned placebo effects aren't useful in actually developing synesthesia.