I’m not in the mood

没有兴致，没有心情

She is not in the mood for talking to him about this topic.

她心情不好，不想跟他讨论这个话题。

I'm upset 心烦意乱

I'm still upset but I know it is for my own good.

是啊，我还在郁闷呢，不过我知道这是为了我好。

Heart sinks

小心脏往下一沉，可想而知有多伤心了。

My heart sank when I saw the amount of work waiting for me.

看到有那么多工作等着我做，我很不开心。

I'm down 心情低落

He is a very good listener and he knows how to cheer me up when I'm down.

他是个很棒的倾听者，每当我心情低落时，他知道如何让我振作起来。

In low spirits

心情很low，情绪低落，英文里用这个短语表示。反之，兴高采烈则是in high spirits。

when I am in low spirit, I always listen to this song, which always bring me new hope.

每当心情低落的时候，这首歌总是为我带来新的希望。

The art of being happy lies in the power of extracting happiness from common things.

快乐的艺术是由平凡提取快乐的能力。