getting up earlier=less daytime fatigue (why & anyone else notice this?)

I've had a problem with fatigue during the day and have noticed that if I wake up early, (before 9am) then I am much less fatigued than usual, it doesn't matter how many hour of sleep I got either. Even if I only sleep a few hours, if I wake up early then I have decent energy for the day.

Does anyone know why this is?
Anyone else experience this too?

thanks!