Anhedonia

Anhedonia is a term in psychiatry used to describe the inability to feel pleasure from activities that are usually enjoyable, such as hobbies, social interaction and sex. It is a symptom of many forms of mental illness, including clinical depression and schizophrenia. However, it can often just be a reaction to stress or severe illness, although it is also exhibited as a symptom of certain physical illnesses such as Familial Mediterranean fever. 
The underlying etiology of anhedonia is unknown, although it is thought to be related to the function of dopamine. 
Anhedonia at Wikipedia
Category:Symptoms