Persistent levels of sadness, helplessness, and disinterest in normal activities severe enough to interfere with a person’s daily functioning.
Example: A nurse can’t concentrate on her work, feels hopeless, and cries at least once a day. She assumes she’ll soon be fired for incompetence, and doesn’t have the energy to care.
Grinnell, R. (2008). Depression. Psych Central. Retrieved on June 3, 2015, from http://psychcentral.com/encyclopedia/2008/depression/