Air quotes refer to the physical act of mimicking the quotation mark symbol (") with one's hands. As in, this:
So, your friend did not use air quotes, he used scare quotes, because he used the quotes in writing, not in person. That was a slip on his part.
Function of scare quotes, according to Wikipedia:
Scare quotes, shudder quotes, or sneer quotes are quotation marks placed around a word or phrase to signal that a term is being used in a nonstandard, ironic, or otherwise special sense. They may be used to imply that a particular expression is not necessarily how the author would have worded a concept. Scare quotes may serve a function similar to verbally preceding a phrase with the expression "so-called", they may imply skepticism or disagreement, or that the writer intends an opposite sense of the words enclosed in quotes.
It seems your friend used scare quotes to signal to you that when he writes "unwind," he does not mean the textbook definition of the word. Here is the textbook definition of "unwind":
To relax after a period of work or tension.
There are several ways to interpret how your friend used scare quotes to distance himself from the above definition. If you don't know what he's getting at, you'll have to ask him directly for his intent. But it is safe to say that it involves something contrary to "relaxation," especially considering the extra attention he called to the scare quotes.
Definition of the idiom, you might as well (do something), according to the Cambridge Dictionary of American Idioms:
There is no reason you should not do something; you may as well (do
e.g., Since you have to wait, you might as well sit down and relax.