The death of a loved one evokes painful emotions in all of us. In uncomplicated grief, a person who has suffered a loss experiences sadness and other difficult feelings, but can continue functioning in her everyday life. In more complicated grief, depression or anxiety emerge, leading to such symptoms as loss of interest and pleasure in one's life, concentration difficulties, self-isolating behavior, irrational guilt and self-blame, and avoidance of reminders of the lost loved one.
There is, clinically, no difference between prolonged intense grief and major depressive disorder. In addition, a person who is already struggling with depression will likely experience a worsening of their symptoms following the loss of a loved one.