I was getting the same way, all the time, before I started this WOE. It felt like I was on downers! It's one of many things that got me started looking at Paleo. Now for the first time in my life I'm not only enjoying working out, but really feeling the need to get out and exercise.
Unless I eat grain or starchy food...then I can kiss that goodbye and it's back to drowsiness and/or migraines.