I read an interesting review article published in Physiology comparing the low metabolic states of non-rapid eye movement sleep (NREM) and torpor. According to the article, all mammals experience NREM sleep patterns during which energy expenditure is decreased and body as well as brain temperatures decline. Animals that experience torpor (hummingbirds, arctic ground squirrels, some mice, bears, etc) have reduced metabolic rates and body temperatures that dip below baseline. NREM and torpor share some commonalities such as reduced muscle tone, less interactions with the surrounding environment and energy conservation.
Although doctors may induce hypothermia in some patients undergoing heart surgery to help protect their tissues, this hypometabolic state cannot be sustained for long without causing damage to the brain or other tissues. Thus, unlike many space-inspired SciFi shows, prolonged suspended animation or synthetic torpor is not yet a viable option for humans interested in space travel or waiting for medicine to catch up with treating an illness. The hope is that by understanding torpor, we may be able to someday induce a synthetic torpor-like state in humans that would be useful for these applications.
Silvani A, Cerri M, Zoccoli G, Swoap SJ. Is adenosine action common ground for NREM sleep, torpor, and other hypometabolic states? Physiology. 33: 182-196, 2018. doi:10.1152/physiol.00007.201