Other forms: postprandially
Anything that's postprandial happens immediately after eating a meal, like the postprandial sleepiness that follows Thanksgiving dinner and leaves your entire family snoozing on the couch.
The adjective postprandial is just what you need for describing that after-dinner drowsiness, a condition that has the official name postprandial somnolence. If you can resist taking a nap after an unusually large lunch, you might instead take a postprandial walk around the block. Postprandial adds the prefix post-, or "after," to the Latin prandium, "luncheon."