Mild/Minor Depression

While symptoms are usually less severe and less numerous in mild depression than moderate and major depression, they still have the ability to cause disruption and distress. Mild depression often goes undiagnosed because many people do not consider the symptoms to be 'bad enough' to discuss them with their doctor or family member/friend.

According to The World Health Organisation mild depression includes 2 of the first three symptoms and at least 2 others.

1. Two weeks of an abnormal depressed mood 
2. Loss of interest or pleasure in activities that used to be enjoyable 
3. Reduced energy, or feeling tired
4. Loss of confidence and self-esteem
5. Feeling guilty and unworthy
6. Recurrent thoughts of death or suicide, or any suicidal/self-harming behaviour
7. Reduced ability to think or concentrate 
8. Agitated or slow movements
9. Disturbed sleep (not enough/too much/poor quality)
10. Change in appetite (increase or decrease) with weight change
11. Decreased libido
12. Unexplained physical symptoms

Mild depression may be felt as an ongoing constant state (aka dysthymic disorder), it may be a brief period (such as 3-4 weeks) or it may be episodic and reoccur at varying intervals.
 
Accurately diagnosing depression when it is mild, and treating it effectively at this stage can prevent the condition from worsening.  There are also a wider range of options to manage mild depression and prevent its reccurrence.

References

The ICD-10 Classification of Mental and Behavioural Disorders
World Health Organisation
1993

Understanding Depression
Maria Prendergast
2006