** 1. when blood pressure is low, heart race tends to increase [physiological explanation]. 2. as female [any hormonal changes]; examination with gynecologist? 3. The cause of low blood pressure was clinically established OR suitable blood tests, radiologic studies, and cardiac testing were done to look for arrhythmias, [if yes] what was the opinion of cardiologist? 4. since she is a teenager thus pregnancy can be ruled out, still look for any endocrinological problem [thyroid, blood sugar, adrenal insufficiency], or for heart problems [heart valves, arrhythmias] 5. diet lacking in vitamin B-12 and folic acid can result in anemia leading to low blood pressure, check with laboratory values, and simply being dehydrated can contribute to the problem so make sure she is adequately hydrated. 6. Low blood pressure is sometimes associated with certain symptoms, many of which are related to causes rather than effects of hypotension: [like fever, heart race in your case] 7. adding electrolytes to diet, good nutrition and treatment will depend upon the underlying CAUSE. PS . Consult your Doctor regarding Dysautonomia [Autonomic Dysfunction] and Neurological examination for cause of hypotension . If they believe that some Autoimmune disorder is the cause of low blood pressure, then prognosis depends upon the pathology of each autoimmune disease. . Among the autoimmune diseases that affect significantly more women are: Hashimoto s thyroiditis, grave s disease, multiple sclerosis (MS), myasthenia gravis, Systemic lupus erythematous [SLE], Rheumatoid arthritis [RA]. [Researchers are investigating why women are more susceptible to autoimmune diseases, in hopes of finding new ways to prevent, treat, and possibly even cure these diseases]