Clinical depression is diagnosed when an individual experiences a severely depressed mood that includes five or more primary symptoms that cause an impairment in usual functioning nearly every day, during the same two-week period.

Primary clinical depression symptoms include:

Feelings of overwhelming sadness and/or fear, or the seeming inability to feel emotion (emptiness).
A decrease in the amount of interest or pleasure in all, or almost all, daily activities.
Changing appetite and marked weight gain or loss.
Disturbed sleep patterns, such as insomnia, loss of REM sleep, or excessive sleep (Hypersomnia).
Psychomotor agitation or retardation nearly every day.
Fatigue, mental or physical, also loss of energy.
Intense feelings of guilt, helplessness, hopelessness, worthlessness, isolation/loneliness
and/or anxiety.
Feeling and/or fear of being abandoned by those close to one.
Trouble concentrating, keeping focus or making decisions or a generalized slowing and obtunding
of cognition, including memory.
Recurrent thoughts of death (not just fear of dying), desire to just "lay down and die" or
"stop breathing", recurrent suicidal ideation without a specific plan, or a suicide attempt or
a specific plan for committing suicide.

Other symptoms often reported but not usually taken into account in diagnosis include:

Self-loathing.
A decrease in self-esteem.
Inattention to personal hygiene.
Sensitivity to noise.
Physical aches and pains, and the belief these may be signs of serious illness.
Fear of 'going mad'.
Change in perception of time.
Periods of sobbing.
Possible behavioral changes, such as aggression and/or irritability.

Childhood Depression Symptoms
Leading Depression Treatment Solutions
Antidepressant Medication Facts
60 Second Online Depression Test
Depression Facts and Statistics