Well, I figured out that the 'energy' I thought I was experiencing on Carnivore was in fact a histamine reaction to bovine gel capsules as I was using for powdered supplements; as soon as I switched back to vegetable capsules yesterday, all the energy disappeared and I hit the same wall I always do on Zero Carb (even with adequate fat and calories). I cooked some liver last night because I was desperate to get some carbs, and it's helped with my energy levels today, but also caused a histamine reaction *sigh*.
So seems like I'm at a bit of a dead-end, since my body needs carbohydrates to function but they're all riddled with histamine, salicylates etc.