Adding more salt to your diet would help increase blood pressure. Good way to do this is drinking lots of broth, soups, etc. your blood sugar may be cycling up and down, which may suggest eating a way that reduces the cycling. To do this, eat low carb diet, moderate protein and balance of calories from fat. Stabilizing your blood sugar will likely help the ups and downs you are experiencing after eating.
Adding salt to your diet is not the right answer. Your physicians seem to be conscientious in ruling out carcinoid syndrome. In the meantime, obtain a consult with a hematologist. Certain rare blood disorders (sickle-cell anemia) destroy the ability of the red blood cells to carry oxygen, albeit only in select genetic populations,. Profuse cold sweats, particularly on the forehead, are the hallmark of cardiac ischemia (lack of oxygen to the heart). Obtain an inexpensive pulse oximeter to check your P02 levels. Another problem could be lack of body capacitance, caused by inappropriate dilation of ther vasculature. Keep well hydrated with electrolytes. I urge you to get a second, and preferably a third opinion, ideally at a teaching hospital. A differential diagnosis can be very difficult and lack of a diagnosis does not necessarily mean your physicians are incompetent.
Thank you for your comments. I have been to neurologists, endocrinologists,gastroenterology each and nothin. My blood sugar are only mildly high at night and fine around 100 all day. Sweating is all day and night. All scans have been negative. I wondering if it is pituitary or the hypothalamus? I have no appetite and don't over eat, drink anything but water. Thyroid checks out fine. I am ready to throw in the towel. I take extra B vitamin supplements with no relief. I can't seem to find any one who can put all the pieces together.