Hello, Khalia. It sounds to me like the food poisoning caused severe and rapid fluid loss from vomiting and/or diarrhea, which led to the neurocardiogenic syncope. The feelings you describe--rapid heartbeat, worse with walking (or other exertion); lightheadedness; hot flashes--are typical of what people experience just prior to passing out. These are also called pre-syncopal symptoms. You mention the Holter Monitor had showed a abnormally fast heart beat (tachycardia). How fast was it? Did the heart rate slow down when you started taking Propranolol? The Neurocardiogenic Syncope Syndrome should not continue after the lone episode of food poisoning. Once the acute illness is over, and once you re-hydrate yourself, things usually go back to normal. People with true Neurocardiogenic Syncope Syndrom have abnormally sensitive autonomic nervous systems, which overreact to the normal signals to vasoconstrict or vasodilate the arteries, or to slow down or speed up the heart rate in response to certain stimuli. If your blood pressure is usually abnormally low (which many normal, healthy 18-year-old women have), then if you are menstruating or dehydrated for any other reasons, your blood pressure could drop low enough to feel uncomfortable symptoms or to pass out. This is one reason a doctor might try Fludrocortisone, a type of steroid hormone made in our adrenal glands that causes the blood pressure to rise by increasing the absorption of salt and water by the kidneys. The other thing we sometimes try for this problem is to promote a salty diet, either by eating salty things, adding table salt, or sometimes prescribing salt tablets. This helps the body s salt and water balance to promote thirst and water retention, which, in turn, helps fix dehydration and helps to keep the blood pressure higher than it naturally is. Depending upon what happens to your symptoms with aggressive hydration and possibly increased salt intake, your heart rate may decrease on its own, and you may not need to stay on the Propranolol permanently. Definitely follow up with your doctor to monitor you for your ongoing symptoms and look for other possible causes of sinus tachycardia, an abnormally fast pulse, such as anemia, hyperthyroidism, ongoing infections, etc. Good luck, and let us know what happens.