I suffer from this. I have a number of physical problems, one being chronic nausea. I have had it from the time I was very young. My other illnesses cause the nausea and I often times end up in the hospital as a result. Over the years, I developed this fear the moment my stomach would feel even a little "off". It's a very challenging problem for me since I am overly aware of my stomach and the moment it doesn't feel right the fear kicks on. The fear then worsens the nausea! It's a nasty circle.
I have not really been able to address the problem since it will always be with me. Unfortunately, nausea and vomiting are a regular part of my daily life. I am trying to work on reducing my fear, but it's a long road and the best I can do is to take it a day at a time.
Sending best wishes to you.