I could not find anyone mention this before, but there is a phenomenon called food coma. It may be also called food fatigue I think, although I am not exactly apt in English. I also often have this when I eat a lot at once and especially sugar rich foods. What is interesting that the depression I feel at the time is exactly like the one induced by POIS. When there is a pre-existing POIS depression it can be especially bad with blurry eyes, sleepiness and the inability to focus on anything or to think at all. Coffee can acutely help in both cases, however later this leads to increased POIS activity. POIS depression tends to be the worst in the mornings when I have not eaten for about 10 hours, so it is hard to imagine a connection. It is true though that not eating anything well before going to sleep I can have better mornings, but when I am feeling hungry I just can’t sleep. POIS also makes me ravenous so it is difficult to restrict myself even if I know that it only leads to depression. Another peak for depression is usually after 9 pm in the evening and sometimes it seems so accurate that it could be more related to the diurnal rhythm than to any food I ate before.
Another thing I wanted to emphasize by this relation is that the depression I feel is not an emotional entity as others may believe when I mention it. Thus it may be important to tell this to doctors to avoid any misconceptions and as something that even healthy people could relate to.