Depression is by far the most common emotion associated with chronic back pain. The type of depression that often accompanies chronic pain is referred to as major depression or clinical depression. This type of depression goes beyond what would be considered normal sadness or feeling "down for a few days".
The symptoms of a major depression occur daily for at least two weeks and include at least 5 of the following (DSM-IV, 1994):
A predominant mood that is depressed, sad, blue, hopeless, low, or irritable, which may include periodic crying spells
Poor appetite or significant weight loss or increased appetite or weight gain
Sleep problem of either too much (hypersomnia) or too little (hyposomnia) sleep
Feeling agitated (restless) or sluggish (low energy or fatigue)