Having a serious winter in Montreal, we always experience the phenomenon of emotional blooming after months of hibernation (gaining weight, depression, too much internet, ...). Bears do it for real, reducing their energy (metabolism) use during the coldest seasons.
They maintain their muscle mass and seem unaffected by an extended inactive state when ready to rumble again. A recent research may in time inspire new techniques that could prove useful in emergency medicine.
More about this via BBC News.