Periodic sadness or temporary depressed mood in response to difficult or painful life events is representative of healthy psychological functioning.
However, depressed mood may be considered a diagnosable condition such as Major Depression when this state is present most of the day, nearly everyday as evidenced by subjective report of feelings of sadness, emptiness or hopelessness or outward signs observed by others, for example, tearfulness, for a minimum 2 week period.
The experience of children and adolescents is often irritable mood.
Alternatively, the primary symptom of Major Depression may be reduced interest or pleasure in most activities (known as anhedonia) nearly everyday, once again through either subjective experience or observation.
Other symptoms that often accompany these primary difficulties include: significant and rapid weight loss or weight gain or decrease or increase in appetite nearly every day, insomnia or hypersomnia, physical agitation or slowness (in response to the mood change), fatigue or loss of energy most days, feelings of worthlessness or inappropriate guilt, problems with concentration and decision making capacity, recurring thoughts of death or suicidal thoughts.
Additionally, the symptoms make it difficult for the individual to function socially or at work or to meet usual commitments.