Earlier quoted context omitted.
This sounds like it could be a diet thing. Have you tried eating different things for lunch to see if that affects your mid-afternoon mood?
Actually, I find the most effective means to not fall asleep after lunch is to just not eat lunch. When and if I do, I'm intolerably tired for the afternoon. It's your body's natural response to having been fed - conserve energy until the next hunt.
I think it's more likely to be due to the energy it takes to break down food (meaning you have less free energy) that causes people to feel sluggish after a large meal.