A sloth's whole world is upside down. It hangs from branches by long curved claws, sleeps upside down (about 15 hours a day!), eats upside down, even has its babies upside down. The body of a sloth is built for it - their fur grows the opposite way from most mammals so that rain runs off them properly.
They are so slow that some of the algae growing in their fur turns into tiny ecosystems of its own. Little moths even live in the fur, eating the algae. A sloth is basically a small forest carrying itself around.
Sloths only come down from the trees about once a week, and only for one strange reason - to go to the toilet. Then they head back up, slowly, slowly, and don't come down again for days.
Despite being slow on land, sloths are surprisingly good swimmers. They can hold their breath for over half an hour underwater - longer than most dogs. In the Panamanian rainforest, where rivers and floods are common, this is a very useful skill.