Final answer:
Severe sub-normal body temperature is called hypothermia. It is a potentially dangerous state where the body's core temperature falls below normal levels. Controlled hypothermia is a medically induced state used to protect organs during certain surgeries.
Step-by-step explanation:
Severe sub-normal body temperature is known as hypothermia. This medical condition occurs when the body's core temperature drops below the normal range, which can be dangerous. The body continuously engages in coordinated physiological processes to maintain a stable temperature, controlled by the hypothalamus, acting as a thermostat. However, during conditions like hypothermia, the hypothalamus's efforts to regulate body temperature can be overwhelmed. Controlled hypothermia, on the other hand, is a medical intervention used to lower the body's metabolic rate during certain surgical procedures to protect vital organs.