Science magazine has a very brief letter reporting that mice which inhale 80 ppm of H2S (hydrogen sulfide, the stuff from rotten eggs) fall into a hibernation-like state with very low heart rate and oxygen consumption. The effect is reversible, so that the mice, when returned to normal air, recover. From what I could gather from the Science letter, H2S shuts off the mitochondrial energy supply, so this should have some similarity to cyanosis? Confusing.
A good BBC link about potential uses for this discovery with humans is here.
UPDATE: I couldn't believe that the mice could survive after being knocked unconscious by H2S. A longer story with a partial explanation is at Red Nova. . The story there is that the balance between oxygen and the H2S is critical. When they give the H2S they have to lower the oxygen a great deal. I have to say, I'm getting a bad feeling about this. Either there is sloppy reporting, or sloppy science, but I still don't have a reference trail to what's going on.