some physical changes, including an increase in metabolism (apparently there's a link between sleep deprivation and metabolism). Anyway, I've only been using the machine for 4 nights, but I already feel like I can't get enough to eat. My metabolism CAN'T have sped up THAT quickly, could it? I'm going to chalk my appetite up to stress β€” it's been a rough week β€” because a change that fast seems crazy.