I have been noticing that I feel the best if I sleep 7-8 hours a night. On the weekends I always sleep in, sometimes up to 10-12 hours and I actually feel worse throughout the day. I don't know why this is, but I'm pretty sure it takes me shorter to feel "awake" on days I sleep less whereas on days I sleep 10-12 hours I don't feel awake for the first 5-6 hours of the day.

Also, I always feel better in the 2nd half of the day. No clue why. One would expect it to get worse towards the evening, but it's the exact opposite for me.