ROLLER COASTER QUESTION!!!!!!!!?

Ok ive loved roller coasters all my life. Ive been a coaster addict ive always known every roller coasters name i make my own blogs about it. Well there has been one thing that i dont get about a roller coaster. You know when you go on those straight down drops and you get that feeling in your stomach. Well see i went to Busch Gardens Williamsburg and i rode Loch Ness Monster. Now the drop is only about 140 feet and my stomach dropped big time. But then i went to Hard Rock park and went on a coaster that was 160 ft tall and was straight down and i did not feel any "drop" in my stomach. Ive always wondered why my stomach drops on some smaller rides but it doesnt drop on any bigger rides. Can anyone please tell me why. Please explain it and i will vote for best answer