Most mammals sleep three quarters of the day and more. If there is nothing else to do - meaning hunting, eating , mating or following nature's call - they doze off. Humans in tests without any possibility to measure time are known to sleep longer and longer, adjusting to 14 hours of sleep plus naps in the end. They also said they had never felt so rested in their life and that it was a new sensation to them.
Western style life has us all undernourished with sleep.