Well, apparently my post didn't get up so I will try this again.
Although I understand that inner ear theory, I believe there is more to it than that. If you are anything like me, I don't eat or drink all that much due to the excitement of going on all of the rides. Because it is normally hot during your trips to CP, you should increase the amounts of fluids you intake. However, most people hit the rides and skip the drink stops. This causes your body to become mildly dehydrated and forces it to use other
liquids in your body. This causes less fluids for your organs to be in and therefore does not give them as much room to move so they cannot press up against your diaphragm as hard (and there is also less circulating in the
organs of your digestive tract so they weigh less and can't press as hard). You can also use the theory of expectation. If you memorize the course and know what is happening all of the time, there is not as much
excitement to look forward to. Anticipation also plays a factor. People love rides and tend to exaggerate their feelings so much that they believe what they are saying, so when they ride them and do not "lose their stomach" as much as their initial ride they will be disappointed. Therefore, when they come back they will not be expecting much and be once again shocked (and excited) when the feeling is just as good as the first time. Which is why some people think that they don't get the feeling as much as they go through the course of the day. And as to the reason why some people get sick... well, the stomach and the liver both are located directly beneath the diaphragm with the rest of your abdominal organs located beneath them. When you go down and your organs are pressed up, well, they smash your stomach. Some people just can't tolerate this feeling I guess.
-------------
2000 Millennium Force Ride Operator!!!