unhappy 不开心的
I didn't realize but he was deeply unhappy at that time.
我没有察觉到他那时非常不开心。
I can see that he's unhappy, but I don't know why.
我能看出来他不开心，但是我不知道为什么。

miserable 非常难过的
We were cold, wet and thoroughly miserable.
我们又冷又湿，难受极了。
Don't look so miserable!
别一副闷闷不乐的样子！

upset 难过的，沮丧的；使人沮丧；肚子不舒服
This decision is likely to upset a lot of people.
这项决定很可能会让许多人不快。
There's no point getting upset about it.
犯不着为此事难过。
I had an upset stomach after eating all those cookies.
吃完所有的饼干之后，我的肚子不舒服了。

depressed 沮丧的，忧郁的
She felt very depressed about the future.
她感到前途无望。
The rainy weather made her feel lonely and depressed.
雨天让她觉得孤独难过。

down 难过的
I feel a bit down today.
我今天有点闷闷不乐。

blue 忧郁的
He'd been feeling blue all week.
他整个星期都郁郁不乐。

gloomy 沉闷的，不悦的
It was a wet and gloomy day.
那一日阴天下雨沉闷无聊。
We sat in gloomy silence.
我们郁郁不乐默不作声地坐着。

frustrated 令人懊恼的
It's very easy to get frustrated in this job.
这个工作很容易令人懊恼。
They felt frustrated at the lack of progress.
没有进展，他们感到懊丧。

a long face 拉长脸，不开心
A long face won't solve anything.
拉长个脸解决不了任何事情。
Why the long face?
干嘛拉长个脸？

down in the dumps 难过的
She's still pretty down in the dumps.
她仍然十分沮丧。
Reshma has been so down in the dumps since her boyfriend left her.
自从她的男朋友抛下她以后，瑞斯曼就一直情绪低落。