怎么了？
What's wrong? / what's the matter.

Explain:
怎么 what
了 (past tense marker)
Notes:
“怎么了？” means "What's wrong?/ What's the matter?" This is used when someone in ill. Unhappy or has some health problem.

我不太舒服。
I feel uncomfortable. / I don’t feel well.
Explain:
我 I
不 not
太 very
舒服 comfortable
Notes:
“我不太舒服。” means “I feel uncomfortable. /I don’t feel well.” This sentence is often used to show that someone is not comfortable physically and healthily, or that something is making someone feel uncomfortable.

病了？
Are you sick?
Explain:
病 ill/sick
了 (past tense marker)
Notes:
“病了?’’ means “Are you sick?” This phrase is usually used when you guess that someone is physically ill or he suffers from a disease or illness. But you can’t say “你有病？” because this always means you hate someone and feel his is very bad.

头疼。
I've got a headache.
Explain:
头疼 headache
Notes:
“头疼。” means “I've got a headache.” This is a common Chinese expression, which is often used to express a pain you feel inside your head to others, and also indicates a trouble.

是不是感冒了？
Have you caught a cold?
Explain:
是不是 yes or no
感冒 catch a cold
了 (past tense marker)
Notes:
“是不是感冒了？” means “Have you caught a cold?” As cold is a very common illness that makes it difficult to breathe through one's nose and often makes one's throat hurt, this phrase is often used to inquire someone if he suffers from a cold when he has some symptoms.

去医院看看吧。
Go to see a doctor.
Explain:
去 go to
医院 hospital
看看 see (a doctor)
吧 [(used at the end of a sentence) indicating entreaty, suggestion, command, etc.]
Notes:
“去医院看看吧。” means “Go to see a doctor.” Chinese people would buy some medicine in a drug store if he thinks it? s not serious. You may say this to suggest him go to a hospital if you think it's better for him to recover quickly.

没事。
I'm OK./ I'm fine.
Explain:
没事OK/fine
Notes:
“没事。” means “I’m OK. / I’m fine.” This phrase originally refers that someone is in good health. Here it is a polite way of expressing oneself. Perhaps he is not very well, but he doesn't want you to worry about him.

不要紧。
It doesn't matter.
Explain:
不 no/not
要紧 matter
Notes:
“不要紧。” Means "It doesn’t matter." This phrase and “没事。” have the similar meaning. Except his family members, Chinese people seldom tell others details about his illness. They don't like to bother other people with his own trouble.

注意休息。
Take a good rest.
Explain:
注意 pay attention to
休息 rest
Notes:
“注意休息。” means “Take a good rest.” It is a common polite phrase, used to show friendship and your concern about the health of your friends, relatives or close acquaintances.

多喝水。
Drink more water.
Explain:
多 more
喝水 drink water
Notes:
“多喝水。” means “Drink more water.” This sentence is often used when one's friends, colleagues, relatives and family members, have caught a cold. It’s believed that drinking enough water is very helpful for treating cold.