That's because they have underlying mania. Once they stop suppressing it with alcohol, the dopamine takes over. The compulsion to move and starve and injure oneself- are symptoms, not solutions.
I obsess about obsession because it seems like the best use of the pathology.
Not that I really have any choice...
I believe that the majority of mental illness is secondary symptoms of common chronic infections. I was a medical librarian, and now I just pretty much constantly research sleep disorders, depression, mania and dementia. This is where I collect my accumulating hypotheses and try to document the atrocities occurring daily in the Infection Industrial Complex.
My goal is not to convince you that my ideas are right, but to show you there is more than one way to interpret scientific data.
Update: After fifteen years of this, I finally think I am right.