心境恶劣障碍（精神官能性忧郁症）是一种慢性情绪失调，属于临床抑郁症范畴。持续时间比重型抑郁症长，但症状相对较轻。

慢性抑郁症是一种轻度的抑郁症。《哈佛健康通信》（Harvard Health Publications）的说法是：「希腊单词dysthymia的意思是『心智的坏状态』或『病态心情』。作为临床抑郁症的两种基本形式之一，其症状比重型抑郁症要少或轻，但持续时间更长。」《哈佛健康通信》说：「病人中，至少四分之三患有临床上的身体疾病，或是另一种心理疾病，像焦虑症、药物成瘾或酒精成瘾。The Primary Care Journal说，慢性抑郁症「人群中的发病率约为3%，且与显著的机能障碍有关。」《哈佛健康通信》说：「慢性抑郁症患者家属之抑郁症早期发病率高达50%」，「大多数患者不能明确指出抑郁开始的时间。」

Dysthymia (/dɪsˈθaɪmiə/ dis-THY-mee-ə, from Ancient Greek δυσθυμία, "bad state of mind"), sometimes also called neurotic depression, dysthymic disorder, or chronic depression, is a mood disorder consisting of the same cognitive and physical problems as in depression, with less severe but longer-lasting symptoms. The concept was coined by Robert Spitzer as a replacement for the term "depressive personality" in the late 1970s.