A lack of pleasant feelings during normally pleasurable events such as social interaction, eating, or sex. This state is caused by a sheer lack of joy during extreme bouts of depression. One of the factors that has been linked to this condition is stress.
Example: He used to be the life of the party, but he never seems happy to see us anymore.
Fournier, G. (2010). Anhedonia. Psych Central. Retrieved on April 21, 2015, from http://psychcentral.com/encyclopedia/2008/anhedonia/