There are no diagnosis that start with the letter J that I'm aware of or that can be found in the DSM-IV-TR. However, there is an amazing psychologist named Carl Jung who I will quote,
"Anyone who wants to know the human psyche will learn next to nothing from experimental psychology. He would be better advised to abandon exact science, put away his scholar’s gown, bid farewell to his study, and wander with human heart throughout the world. There in the horrors of prisons, lunatic asylums and hospitals, in drab suburban pubs, in brothels and gambling-hells, in the salons of the elegant, the stock exchanges, socialist meetings, churches, revivalist gatherings and ecstatic sects, through love and hate, through the experience of passion in every form in his own body, he would reap a richer stores of knowledge than text-books a foot thick could give him, and he will know how to doctor the sick with a real knowledge of the human soul."
As writers this applies to us as well. In order to truly write the great stories we need to have experiences. No we are not going to fly spaceships or have magical powers but we can have human experiences that will inspire us and make us step outside our boxes. We can open our minds to those things that go beyond what we have seen a million times and write about the human condition in all its forms. Also, we can put down the books that teach us to write and start writing!