From my experience… I need some 7 hours minimum. Less sleeping time means feeling very tired, means bad humour, means feeling I’m loosing some precious time. In short, we really need to sleep if we want to feel happy (first!) and relaxed. I live in Spain, and here we have a “tradition”: “Siesta”! We take a nap, after lunch, whenever it’s possible (weekends). (Note ours lunches are the opposite to a light meal.) There are even some studies about the benefits of the nap!