I find that my fatigue relates to the quality of sleep I get, not the quantity. I can get 6 hours of good sleep and wake up doing great. If I struggle to get good sleep, I can sleep for 10 hours and be fatigued all day.

If I am struggling to get good sleep, I do better getting up and changing my pace. Watch some TV or browse online. Then, when I am feeling dead sleepy, going back to bed. I also need to be very comfortable in bed. A good mattress and soft pajamas with no strange sensations make all the difference. I can go to sleep on my back and wake up in the morning in the same position. It takes discipline to learn these sleep disciplines but it is worth it.