This sounds like a really interesting idea to explore. I can definitely relate to it coming in waves. I don't think I've ever been hungry for a very long time but I've heard that after a few days pangs of hunger sort of go away. Maybe because at that point in a survival situation they are inhibiting your ability to find food more than they are motivating you. It's interesting to think about how your body communicates with your mind. I think sleepiness/fatigue is similar. You can't just query your energy levels, your body has to send these sporadic alarms that are enough to distract you without being debilitating.