7 ways to overcome your noonday devil and stay on task

Q: Often in the early afternoon I find myself hitting a wall in my work activity. After working at my desk from 7:15 or 7:30 a.m., I lose energy, then focus, and then I find my attention drifting to less than important tasks. I think my team senses my sluggishness. By the end of the day I am behind and I end up staying late to catch up. What can I do to stay more on task?