Food Coma - Postprandial somnolence You get a bit tired after a large meal, due to your nervous system going into a more relaxed state. This can be greatly amplified biochemically if your meal was very heavy in carbohydrates (and for most hams, we know it was.) The pancreas goes into overtime pouring insulin into your body to try to get the blood glucose back down. One of the cascading effects is a large increase in serotonin in the brain. Basically your body needs to call on all its resources to convert your giant meal into body fat.