Short answers, pulled from the story.
Hibernation is a physiological state of dormant inactivity characterized by minimal activity, metabolic reduction, low body temperature, slow breathing, and drastically reduced heart rate. This seasonal heterothermy allows animals to pass through winter months when food becomes scarce.
Obligate hibernators include European hedgehogs, monotremes, marsupials, and many rodents that enter dormancy spontaneously regardless of ambient temperature or food availability. Facultative hibernators like chipmunks and black-tailed prairie dogs only enter dormancy when cold-stressed or food-deprived.
Bears lose 15 to 27 percent of their pre-hibernation weight using stored fats for energy while recycling proteins and urine to stop urinating for months without muscle atrophy. They stay hydrated through metabolic water produced in sufficient quantities to satisfy needs despite no drinking.
Thrinaxodon lived roughly 252 million years ago as an ancestor of mammals exhibiting early hibernation forms. Hibernation likely evolved simultaneously with endothermy during the transition from ectothermy to warm-bloodedness.
Hibernation induction trigger proteins isolated from mammals have been used to study organ recovery rates since 1997 and allow scientists to manufacture these proteins in laboratories without animal euthanasia through recombinant technology. Researchers explore inducing human hibernation to save lives of seriously ill or injured people temporarily until treatment arrives.