Why am I more awake with less sleep?

When I get only 3-5 hours of sleep I tend to be more awake and function better over all because of it. When I get the recommended amount of sleep I am extremely groggy and can never focus entirely. The only other amount of sleep that produces an awake, alert feeling is if I sleep for literally half the day, and that only happens on days when I don't have to wake up and just sleep until I can't physically sleep anymore, I normally get 12-16 hours then. Any ideas why?