It could be due to not eating or the specific chemicals in the pill or both. I get headaches from not eating for long periods while sober, so they could very likely happen after fasting all day then rolling all night and not eating while your body is running in high gear. If you want to keep a relatively empty stomach for when you drop, eat a light snack of carbs, like sugars or starches, at certain intervals of time. They digest and leave your stomach quicker, but still provide you with some nourishment. I find that after I've come down, the sooner I eat any substantial meal, the better i feel, whether I'm actually hungry or not. Other factors are less controllable, such as certain adulterants or combinations of them that can cause harsher comedowns.