Not OP, but I agree with you that we need different words. Because what OP is doing is not starvation (till their body is actually wasting away). Having done a few 3 days fasts myself, I can attest to feeling a euphoric energy around day 2 where I felt lighter, and sharper. I have been told it isn't universal, but from the content I have been consuming it has something to do with brain switching to consuming ketones.

Which actually brings me to another point; the brain does not run exclusively on carbs (glucose) - it absolutely has the ability to (and does) functions well on ketones. This is why ketogenic diets can work for many people.

But yes, there's lots of bio-chemical mechanisms that get kicked off when you're fasting for an extended period, so it could be something else that's unique to the people who experience the euphoria.

I am not sure if you've come across this concept, but "Metabolic Flexibility" seems to be trying to explain some of the "after burner" affects of switching around my dieting habits. Where I am no longer exercising strict caloric restrictions, or fasting on a regimen, but I am still observing some of the benefits of when I switched over. (Less bloating, more energetic even after a large meal, less voracious appetite on normal days).