1. Is something on your mind? / Do you have something on your mind? /What's on your mind? 你担心什么呢?

　　Be on a person's mind 意思就是“有什么挂心的事”。Note: This has a milder, easier tone but can still apply to serious problems such as job dissatisfaction or even job loss or marital problems.

　　2. Why are you so glum? 你怎么看起来闷闷不乐的？

　　Note: Spoken in a mild tone, it sounds friendly and caring. Often used when someone is feeling blue or mildly depressed.

　　3. Why the long face? 你怎么看起来这么疲惫？

　　Note: Meaning "Why do you seem so unhappy?" The complete sentence would be "Why do you have such a long face?" (But, no one would ever say that.)

　　4. You're not yourself today. / You don't seem to be yourself today. 你今天有点心神不宁。

　　Note: Mild way of saying "you don't seem to be in such a good mood today" or "you don't seem to be feeling so well today". People also say "Sorry, I'm just not myself today" (对不起，我也不知道今天我是怎么了), as an excuse after not performing well on the job.

　　5. Who are you irritated with? 谁惹你生气了？

　　Be irritated with 的意思是“为……而急躁，为……而发怒”。Note: This is used only in a very specific situation where someone is having a problem with another person.