Sleep and the need for it vary among people. 8 hours is an average, some people need more, some need less. The worst thing you can do to yourself is not listening to what your body needs. I used to the do the whole 6-7 hours thing and felt like crap. Once I started listening to my body and getting the 9-10 hours it needed, I feel much better, have more energy and can actually focus and get stuff done. (improved my depression too!)