It is a known fact that people get drowsy after eating. Postprandial sleepiness is very common, especially after eating a large amount of food. The digestion of the stomach contents draws extra blood to the GI tract, thus leaving less for the rest of the body and especially the brain, which needs a large amount. There is also a dip in blood sugar right after eating a large meal, just before the blood glucose rises due to digestion of the food.
"Postprandial narcolepsy" is a humorous term commonly used by professors in medical school to refer to the state of medical students' attention in classes immediately after lunch. Professors never want to teach the 1 o'clock lectures, because the students tend to be very sleepy.
But, if all other possible causes of the sleepiness have been ruled out, unfortunately there is not much that can be done. You may need to eat smaller meals, and thus eat more often. Trying to avoid very large amounts of food when you eat. Other than that, it will be just knowing that there is nothing physically wrong with you and that this is just the way you react to digestion. Consuming stimulates (eg caffeine) may be of some help. If the situation is very severe, interfering with your occupation and livelihood, you may be able to get a physician to prescribe a mild stimulant. However, this is not ideal, due to the fact that these medications have a high potential for addiction and abuse.
But, again, make sure there is nothing else going on before attributing it to just "postprandial narcolepsy". You may need to have a thorough physical exam with specialized testing. You might want to speak with a neurologist to see if an exam and testing would be warranted.
what you said is correct, I can accept if this sleepy mood disturbs me for half an hour but it will spoil more than or around one and half hour that means I am loosing a very long precious time in my daily job. As you advised, should I meet a neourologist, will all these testing very costly?
waiting for your reply