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.
