Hi, I'd like to help you with your question.
It sounds like your wife might be suffering from anxiety and panic disorder. It is very common for people who develop anxiety and panic to feel like something is wrong physically. Often, they are sure they have a brain tumor or are having a heart attack. This is because the symptoms of panic and anxiety are so distressing.
It is good that your wife is going to be seeing a doctor. She needs to have the necessary tests to rule out any possible physical cause. Along with being sure there is nothing physically wrong, it will give her reassurance that she is ok.
If she is cleared physically, then the doctor can refer her to a therapist for an evaluation and treatment. Cognative Behavioral therapy (CBT) has proven to be very effective in helping those with panic and anxiety.
Also, she can try reading a book called The Anxiety and Phobia Workbook by Edmund Bourne. It is an excellent book full of reassuring information and ways to help yourself overcome anxiety. You can get it on Amazon.com or her local library may have it available.
Mostly what she needs from you is reassurance. She needs to know she is ok and that there is help out there for her. It is hard to be supportive from a distance, but any kind words and reassurance will help.
I hope this has helped you,