Adding 什么(shénme) to the end of an adjective (or less frequently to a verb) can be used to form a [http://en.wikipedia.org/wiki/Rhetorical_question| rhetorical question]. For example, in the phrase 你急什么？"what are you worried about?," the speaker is implying that there is no need to be worried.
Adj.／Verb + 什么 + (Adj.／Verb)？
Like in English, "what are you worried about" can be a rhetorical question, and can also be actually inquiring about what exactly the listener is worried about. The same is true in Chinese, so context and tone of voice is important in understanding what the speaker means.
If the adjective or verb is repeated after the 什么 as in the 3rd and 4th example, it acts to give further emphasis. It almost has a tone of incredulity, a bit like "what on earth are you worried/anxious about?" Generally only single character adjectives can be used in this way.