re: If you quickly walk 6-8 miles a day would you consider that a worthy work-out?

I feel ya. I'm a shift guy myself and 7 hours are hard to come by sometimes. I drag arse quite often and need sleep catch up days, but I can certainly tell when I'm well rested vs. when I'm not. Have you tried taking a multivitamin? The bottom line is if your getting enough rest, eating decent, and getting exercise and you still feel lethargic all the time, it's time to get checked. Screw the antidepressants. Test levels would be my next stop if you truly are doing the other things listed.