You maybe have heard someone who's had a really long day say that they just want to curl up and hibernate for the rest of the weekend. While humans don't really have the ability to put ourselves in a state of continuous slumber for more than a couple of days (maximum), hibernation is a very real thing that occurs throughout the animal kingdom. It tends to happen over the winter, when food is scarce. The metabolic processes slow down to consume dramatically less energy, and certain animals (most famously bears and squirrels) spend the summer months getting fat and storing up food, which they then slowly burn off during their long winter's sleep.
For animals that do hibernate, it's vital to their overall well-being. Not being able to hibernate means having to burn a lot more energy on a daily basis just to stay warm. Although bears are not true hibernators by the strictest definitions, they do sleep through most of the winter to save energy, only waking up and coming out for brief interludes if it gets warm enough before quickly returning to their dens.
Fifi is a 30-year-old bear who has never had a chance to hibernate the way bears should. She was purchased by a Pennsylvania zoo in her childhood and spent the next 10 years being forced to perform confusing tricks. After the zoo closed, she was locked up in a small, rusty cage built on a concrete slab for the next 20 years. When PETA (People for the Ethical Treatment of Animals) found her in 2015, she was almost on the verge of starving to death. Today, thanks to their efforts, she has been living free for nearly a year and was able to hibernate for the first time in 30 years.
Wait until you see how good she looks today!