Sinking Feeling In One's Stomach

Today I got that sinking feeling in ones stomach when I thought that I was going to hear some bad news (intuition was correct - latter on I did) and I wondered what causes this feeling and why we get it. Looking it up, I found that this feeling was caused by strong emotions: anxiety, nevousness, fear. (Fear was an interesting one, it probably explains why you get a similar feeling just as you start to descend a roller coaster hill, or are in free fall) Anyway, I failed to find out what bodily response is the cause, but I hypothesize that it must do with the flight of fight response, and our bodies shutting our stomach down.