At least five of the following symptoms must be present during the same two-week period (according to ICD-10, less than a two-week period if symptoms are severe and of rapid onset): 1. depressed or irritable mood, 2. anhedonia, 3. significant decrease or increase in weight or appetite or failure to make expected weight gain, 4. insomnia or hypersomnia, 5. psychomotor agitation or retardation, 6. fatigue or loss of energy, 7. feelings of worthlessness or inappropriate guilt, 8. concentration difficulties or indecisiveness, and 9. thoughts of death and/or suicide attempts or ideation.
See Anhedonia, Dysphoria, Neuroticism, Internalizing disorders/problems