Chronic, low-grade depressed feelings are to disorder as moderate, recurring mood swings are to disorder.

Chronic, low-grade depressed feelings are to "dysthymic" disorder as moderate, recurring mood swings are to "cyclothymic" disorder.

Dysthymic disorder is a genuine condition of interminable discouragement, which holds on for no less than two years (one year for youngsters and youths). Dysthymia is less intense and serious than significant depressive issue. 
In cyclothymic disorder, temperaments swing between brief times of mellow wretchedness and hypomania, a raised disposition. The low and high emotional episodes never achieve the seriousness or length of significant depressive or full insanity scenes.