This extreme form of grieving is called complicated grief or prolonged grief disorder. For over a million people a year
...becomes what Dr. M. Katherine Shear, a professor of psychiatry at Columbia, calls “a loop of suffering.” And these people, Dr. Shear added, can barely function. “It takes a person away from humanity,” she said of their suffering, “and has no redemptive value.”Research has shown that such grief can become a mental disorder quite as debilitating as Depression or PTSD. Research shows that it can. For susceptible people such prolonged grief can predict sociality, a higher level of substance abuse, cigarette and alcohol consumption better than can a diagnosis of depression can.
The New York Times science section has an interesting report on this disorder. It apparently is likely to appear in the Diagnostic and Statistics Manual of Mental Disorders (DSM-V) scheduled to be issued in 2012.