The ammonia/NPN problem can cause folks to fall asleep after an offending meal, after all or most meals if food quality and health sufficiently poor.
This happened to me for years, was told it was blood sugar, but the corrective measures for that did not solve problem.
Adding the alkalising drink and detox baths, changing my diet, getting a refractometer and looking for the highest blurry/fuzzy readings i could find has entirely solved this...EVEN IF I AM EATING ALL CARBOHYDRATES, which is what the other theory said was the problem. Even the occasional junk food carb meal does not throw me now!
Sadly, my elderly father had struggles with this for decades. He is so marked by the Depression that he is a tightwad regarding food expenditures, and so set in hos ways he will not learn the principles here. Sad...otherwise I am sure he would do well into his 100's.