There's a new study linking low levels of Hydrogen sulfide (80ppm) to induced, completely reversible torpor in mice.

The mice enter a hibernation state, reducing their oxygen intake by 90%.

Absolutely amazing. If this scales up to humans, we could see a radical change in the way surgery is done, as well as long distance space flight. Imagine inducing hibernation in the case of a heart attack or stroke until you can get to a hospital.