Can you sleep with unrested legs?

Fast asleep with hanging legs!

Horses can sleep on their legs. 

Humans need to rest legs to sleep properly.

But here is this lad, fast asleep in a public park with his legs hanging on to ground, while he is comfortably fast asleep. Interesting thing is he has chosen worst location and bench. There were better locations and benches. Perhaps he was too tired to look around and stumbled upon the very first one.