The following are the symptoms for depression:

Depressed mood most of the day, every day
Diminished interest or pleasure in all activities, most of the day
Significant weight loss or gain
Insomnia or hypersomnia
Psychomotor agitation or retardation
Fatigue or loss of energy
Feelings of guilt of worthlessness

(I have a feeling of worthlessness when reading some of these symptoms, but not due to that of my own )