After eating, the body diverts blood flow to the gastrointestinal tract (the organs that work on digestion). Because more blood flow is traveling to the GI tract, this detracts from blood traveling to the brain. This can lead to drowsiness and lethargy, and is considered to be a normal finding after eating. Eating smaller portions and eating more frequently can decrease the feeling of lethargy after a meal. Also, evaluate the food that you are eating because certain foods have a proclivity towards making us feel drowsy. Some people believe that we feel tired after thanksgiving dinner because turkey has a high concentration of tryptophan, which is considered by some to be a natural sleep aide. Also consider light exercise after a meal, this may get your blood flowing and decrease the drowsiness you feel. If the symptoms you are having have been going on for a long time, and have not worsened or changed recently, this is likely a normal finding. If symptoms continue to worsen, or to receive more information on this condition, it is recommended that you visit your primary care physician
who can better evaluate your specific medical history and presenting symptoms and decide whether further workup is warranted.