Entry in progress—B.P.
 
Wikipedia: Postprandial somnolence
Post-prandial somnolence is a state of drowsiness or lassitude following a meal. Post-prandial somnolence has two components – a general state of low energy related to activation of the parasympathetic nervous system in response to nutrients in the gastrointestinal tract, and a specific state of sleepiness caused by hormonal and neurochemical changes related to the rate at which glucose enters the bloodstream and its downstream effects on amino acid transport in the central nervous system.
   
Urban Dictionary
food coma
May 11, 2006 Urban Word of the Day
The feeling of listlessness, bordering on sleep, that one feels after eating a large meal, often caused by a rush of blood to the stomach and intestines during food digestion.
Man, we ate the whole Pupu platter and now I’m slipping into a food coma.
by Cap’n Sweaty! Oct 9, 2003
   
The Online Slang Dictionary
food coma
the tiredness experienced after eating a satisfying meal.
. Each [Thanksgiving], I gorge myself full of turkey, stuffing, brussels sprouts, string beans, and mashed potatoes and then sleep off my food coma on the couch with football… blasting in the background.
—“Food for Thought: A Makeshift Thanksgiving”, The McGill Tribune, Adam Levine, 11/24/09
   
4 March 1992, Chicago (IL) Sun-Times:
Before the food coma kicks in, be sure to peruse…
   
3 January 1994, USA Today, “Healthy new year includes a vow to lighten up” by Nanci Hellmich, Life, pg. D4:
“I eat 1600 calories a day and 20 to 25 grams of fat except when I’m in New Orleans (his hometown), where I wake up in a food coma.”
 
6 January 1995, Greensboro (NC) News and Record, “You can pinch a holiday inch” by John A. Nagy, pg. D1:
Having shaken off the food coma they slipped into before Christmas, people are awakening to discover a pudge from all that fudge and other holiday goodies.
 
22 November 1995, Fort Worth (TX) Star-Telegram, “Leftovers: The very best part of Thanksgiving,” Food, pg. 1:
By tomorrow’s Cowboy kickoff, most of us will be well into a food coma, dozing off between scores.
     
International - Chowhound
With dinner, we had a nice bottle of some California Viognier—can’t remember what, though, as the turkey sent me into the usual food coma.
(...)
Rachel M. Nov 23, 2001 09:08PM
     
New York (NY) Times
Well
Ate Too Much? Tight Pants May Be the Smallest Worry
By TARA PARKER-POPE
Published: November 20, 2007
(...)
Dr. Goldberg says the digestive workout may also explain the “food coma” many people experience after a big meal. Although popular wisdom holds that Thanksgiving drowsiness is caused by tryptophan, an amino acid found in turkey, Dr. Goldberg notes that the amount isn’t significant enough to affect most people.