I used to have something like this problem, and it turned out to be very simple: hunger. I had a bad habit of not eating when I was deeply into something (or deeply stressed), and my body would simply run out of fuel. I think there is something weird about my physiology that causes me to not notice hunger as much as others. So I wouldn't feel super hungry, but I'd get this spacey, apathetic, faded feeling and have tr…
I just worked for 16 hours on nothing but a hot dog, a candy bar, and a granola bar. Even though I feel almost dead right now, I'm still not very hungry.