The close matching of energy demands to delivery is fundamental for survival. When a saber-toothed tiger jumped out on one of our primitive ancestors, they would need to put in an Olympic-performance sprint requiring maximal energy delivery.
On the other hand, resting up in a warm nest means energy delivery can be reduced. This balancing all happens courtesy of the adrenal and thyroid glands.
Broadly speaking, the thyroid gland base-loads to establish the basal metabolic rate, and the adrenals fine tune. For a seconds- to minutes-level response we have adrenalin, which may be followed by a minutes- to hours-level response determined by cortisol.
Hibernating bears have low levels of thyroid hormones; we see levels of thyroid hormones in humans