I too feel pretty tired by the end of the day and sometimes end up having what i call a 'nanny nap' in the afternoons.
Being a night person I dont usually go to bed until at least midnight on most nights then I get up late and feel I have wasted half the day away. But I generally find that I can go through the day better if i only have about 6 hours sleep.
I think the amount of sleep you need varies from person to person. On the nights I only get about 6 hours I dont need to sleep in the afternoon and I feel energised to do a workout or something physical. However on the nights I have 8 hours or more sleep I feel so lethargic and it takes me forever to get motivated to do anything.
I think you need to experiment with how many hours sleep you need a night and go from there...