This can be one of the symptoms of dysautonomia, so many symptons with it.
glen
*Bingo* If I may expand on Glen's point.
Dysautonomia causes many dysfunctions, including
excessive blood pooling in the stomach when eating - hyperemia.
The more you eat, the more blood is diverted to the stomach - and thus the weaker patients with dysautonomia can feel to the extent they may faint (syncope) or nearly faint (pre syncope symptoms), feel totally exhausted and have to lay on the floor, or get 'motor' dysfunction such as suddenly weakend power in the arms/wrists/hands to the extent people have to eat with their hands (instead of using knife/fork) as their hands cannot maintain the power to 'grip' the tools needed to usually attempt to continue to consume a hearty meal with family/friends.
When blood goes to the stomach, less blood is available for the brain and the heart - and so profound weakness often ensues in person's with this problem. Also remember many people with ME CFS have a lowered blood volume - compounding the problem further. One symptom of both allergy and dysautonomia is anxiety/panic symptoms/adrenaline rushes. See if this happens, this can be related to, or indeed not related to hypoglycemia - as many people 'wait' until supper time to eat a meal (and thus are running low on blood sugar) and can accidently 'freak out' whilst eating - wrongly then thinking they are allergic to something. So a number of causes are possible here. Allergy/Dysautonomia/Glucose problems. Even more complicated is one does not have to be a diabetic or suffer from 'true' clinical low blood sugar (hypoglycemia), one can just be sensitive to dips, drops in glucose. A way to prevent this is to eat regularly (not wait for hours for main meals), avoid high carbohydrate snacking (chips, chocolate, candy), and carbonated sugary drinks.(coke, 7up etc).
So back to the circulatory issues.
Anyone who eats in hot weather the summer, may be able to remember feeling drastically worse - this is precisely because of the heat. (In hot weather, say 25c+ internal room temperature) when consuming food - all of these problems are much worse as blood is being diverted already to the skin to reduce body core temperature on a hot day. So eating a large meal on a hot day is going to really cause a big time reaction, especially if one is not hydrated enough.
So add a dysautonomic response, add low blood volume, add the profound weakness of ME and cerebral (brain) low blood flow - and you get an almost 100% guarantee you will feel worse when you eat, especially when eating a large meal or a heavy meal (e.g. meat), vs something light like a sandwhich or breakfast cereal.
From a personal view point, it was one of the first symptoms I ever noticed. It only happened to me in the evenings. I never put two and two together and realised in the evenings I ate the largest meal of the day. I (wrongly) presumed it was some 'weird' ME type allergy. It was in my case, simple faulty hemodynamic (circulatory) response to eating.
This problems is also seen in the elderly, who classically pass out or go to sleep after a large meal at family gatherings - unlike children who tend to race around totally unaffected!
1) The simplest way to counter act this is to eat smaller portions of food, little and often.
2) Other ways could include wear constrictive vascular stockings (flight leggings) to attempt to try and 'squeeze' blood back into you upper region. These are somewhat uncomfortable, but can cause significant increases in mobility when tried.
3) The most drastic method, (only after a physician diagnoses dysautonomia/vaso vagal syncope) would be to have injections of something like Octreotide- which targets the 'splanchnic bed' (blood pooling site where the blood is rushing to).
Having said that, if one does not have dysautonomia, then feeling ill after meals with more 'conventional' food intolerance or allergy symptoms may well be the reason and should be looked into if troublesome.