You could look into histamine intolerance. Chicken livers are generally considered higher in histamine compared to most other fresh meats. Have you noticed a similar reaction to anything else like fermented foods or tinned fish? If so, it would point in that direction.

Vitamin A and copper could be an issue as well if you are supplementing either of those in addition to eating chicken livers, but this doesn't seem likelyl. You mentioned you are doing this for your huge protein breakfast, so perhaps you are just eating too much of an incredibly nutritionally dense food which isn' really comparable to straight muscle meat. It is possible to get too much of a good thing (i.e. polar bear liver). I can't eat more than a few chicken livers in one sitting, and usually downgrade prtions when I'm eating organ meats. Very rich stuff, I just don't ever crave more than a little. My only other idea is that the chicken livers, if they were from the same batch, had gone bad or were cooked too rare (probably a bad idea with factory farm chicken).

It's possible that you react to the gluten or soy the chickens have eaten. I get really tired when I eat meat and eggs from soy-fed chickens.

It's no problem to get soy free meat/eggs, but to avoid even traces of gluten is really difficult, since even pastured chickens usually have a lot of grains in their diet.

Jeannine, how much liver do you eat at a meal? And are the livers from chickens that roam around and eat bugs, or are the livers from chickens which are fed grains and "mystery foods" and given all sorts of antibiotics and who knows what? I really notice a difference in how I feel if the liver is from pastured chickens.

Do you get the same reaction to beef or veal liver?

I like to eat an ounce of liver at a time, or just a tiny bit more, several days a week. I eat egg yolks, beef bacon, or cheese to fill out the protein amounts for the meal.