Why the koala sleep more than twenty hours in a day?

The koala only gets up for have lunch and then sleeps and sleeps.The koala lives in the jungles of Australia and it eats usually eucalyptus.These leafs have got a little bit calories,so it means,little energy and the koala needs to sleep for not to spend his little energy.He doesn't get up for drink because the eucalyptus's leafs are 50% water.The meaning of the word koala is "someone who doesn't drink".