What Causes Shivering Immediately After Having Food?

My wife trembles immediately after eating, no matter what she eats. She has not been diagnosed with diabetes, but her Dr is closely watching her A1C. She is 60 yrs old, 5'2" 180lbs, mild hypertension controlled with meds(Carvedilol and Irbesartan). She also has gastroperisis, RLS, and sleep apnea.