How to refer to 'depression' in Chinese? Depression is a word used to describe a 人 who feels a sadness that is buried deeply in heart and mind. 

What word is used to refer to this kind of depression?

If you can think of any idioms or sayings that relates to the word 'depression' in Chinese, I would appreciate your sharing of it in the comments too.
The common term would be 抑郁。
There is a type of mental disorder in that name, called major depressive disorder.
However, if you are not referring to the disease, you would say

我觉得有些沮丧
我觉得有点压抑