Nitrogen leaks in a typical factory, for instance, displace an enormous amount of useable air by binding with the oxygen in it.http://www.chem.purdue.edu/chemsafety/Chem/ln2.htm
1L of it that is spilled will result in 24.6 cubic feet of gas, which then displaces 5-6 times that mass of breathable air. In seconds. You won't feel light headed since our bodies naturally ignore nitrogen changes(since it's mostly what "air" is made of) - you'll just pass out and die. It's a lot like carbon monoxide that way, just it gets out of hand very quickly when things go wrong(the freezing body parts and substances exploding from thermal shock and such aside).
You're much better off experimenting with thermoelectric cooling instead. You can easily get virtually the same results with far less risk.