I agree with this. If I eat smoked meat (even naturally cured) or meat that has a lactic acid starter I will get a "cold" or a "flu" but it is like you said only a bad reaction to what I ate. Other allergy foods can do this as well but these ones seem to be the ones I react to the strongest.
Yes. Often didn't sleep/wake easily, had chronic headaches, head and chest congestion, sore throats, ear infections, asthma (untreated until 20's). Migraines at 7. Tonsillitis at 9. Digestive issues at 11. Rapid weight gain starting at 12. PCOS and more frequent migraines at 14 At 15, began falling asleep in class, esp. if hot or after meals (which raises body temperature), regardless of time slept or desire to stay awake. Moments of low energy began at 15; in early 20's, working 6h/day sometimes felt exhausting (but I can't be sure it wasn't caused by lab chemicals).
However, I also dealt with depression, anxiety, and possibly autism. Home was not safe/supportive. Daily school bullying from 9-15. That led to excessive hyper-vigilance by 10 and severe depression by 14. Anxiety correlates to digestion, depression to energy, autism to... a lot of things (maybe sleep issues, PCOS), tonsillectomies and many other factors to obesity, and there are indications that child abuse leads to heart problems. So, I can't easily pick apart what was inherent low immune function and what was triggered by circumstance.