Welcome to HCM!
I have gone through your question carefully and after giving it adequte consederation and from all the information you have given here, I feel that you should go and meet a cardiologist at least once.
The brownish saliva and
chest tightness, abdominal cramping can all take place in soem cardiac cause. Moreover, any
respiratory tract problem which may be causing these are almost ruled out coz you have no cough, cold /flu....
Had I been your doctor, I would definitely do an ECG, Chest X ray, ECHO, along with routine
blood test. An
ultra sound abdomen can tell if there is any other abdominal problem.
Till you meet doctor please avoid sternous activities/ quit
smoking and drinking alcohol completely (if you use them).
You have not mentioned your age and if you have any other disease, so, at present I cannot relate your presentation to anyhing more.
Hope this answer helps you in successfully dealing with this problem.
Feel free to ask more queries if you need.
Dr. Manisha Gopal.