Digestion requires that a large percentage of your bodies blood supply go to the stomach and intestines, rather than the rest of the body. This happens normally when you consume food. (in my family we refer to this feeling as "imobilo", as in an imobilized feeling or sluggishness. Blood supply that normally goes to your brain and body is shunted to this are for digestion. I think that it is just emphasized in contrast to the fast when you begin eating agin. hope this makes sense - I would say it is normal for you to feel this way. That is part of why it is suggested to ease your way back into food with easy to digest foods. (fruit and cooked veggies are easiest to breakdown). You will experience more of the sleepies with anything that requires a lot of digestion. hope this helps.