black dog
noun [ S ] uk/ˌblæk ˈdɒɡ/ us/ˌblæk ˈdɑːɡ/
the black dog 黑狗（抑郁症的一个代名词）
a way of referring to feelings of depression (= great sadness and lack of energy)
There were times when he wrestled with the black dog and couldn't write. 有时他不得不与心中的黑狗较量，无力写作。