When animals hibernate, their heart rate and respiration decrease and they lose consciousness. Why do some animals hibernate?

Animals hibernate to avoid a certain death due to seasonal changes which make their environment inhospitable due to temperatures, like extreme cold and/or other weather conditions, like no rain for many months. One of the most notable species that hibernates are bears. Bears and other animals go in search of food supplies during the end of summer and fall seasons in order to amass as much fatty tissue as possible. These fat stores will be their main energy source while hibernating. As winter is incredible harsh, bears and other animals find areas for prolonged shelter, like a cave or sturdy nest. When they wake up in the spring, bears and other animals are extremely hungry due to the use of their fat stores to maintain basic functions like heart rate and respiration, and having not eating for literally months.