There's different sources of energy. I remember reading this:
Scott H Young » Energy Management
Note the part where he talks abuot the different kinds of energies: Physical, Mental, Emotional and Spiritual.
I've got a copy of that book and I'll start reading it soon. I too have noticed the problem that you're talking about.
Do you take a day or two off to relax every week? Perhaps some sharpening the saw regularly is in order.
I hope this helps.
