Normal symptoms of grief include:

A person with chronic grief experiences and displays all the symptoms of normal grief, but the symptoms are more pronounced and may be more prolonged. http://www.comfort-for-bereavement.com/ChronicGrief.html

This article has some very interesting information about Chronic Grief and the factors that may cause it:

http://www.caresearch.com.au/caresearch/ClinicalPractice/PsychologicalSocialSpiritual/BereavementandGrief/ComplexGrief/tabid/1346/Default.aspx

A Systematic Review of the Literature on Complicated (/Chronic) Grief:

http://www.health.gov.au/internet/main/publishing.nsf/Content/palliativecare-pubs-rsch-grief