I'm sorry your diagnosis has delayed by so many years. A positive Tilt Table Test in the way you describe is indicative of a Dysautonomia, specifically Neurocardiogenic Syncope (also called Neurally Mediated Syncope).
It seems that you are responding appropriately by laying down, and raising your legs when you feel an episode coming on. This will help to restore blood flow to your brain more quickly. Even if it doesn't prevent the episode, it is likely to shorten it. Additionally, there are medications available to treat some of the symptoms.
It's much less common for the episodes to occur while in a supine position, (such as while sleeping), but not entirely impossible. Just the same, I would recommend a full workup by a Cardiologist, as well as a Neurologist to be certain there isn't anything else causing your symptoms.
The fatigue you describe is a very normal symptom in various forms of Dysautonomia. If the patients heart rate or blood pressure is too low to support much physical activity, the individual will undoubtedly feel fatigued. Do you have a home blood pressure monitor? It may be helpful to make a log of these readings for your doctor. In POTS, (another common form of Dysautonomia), the heart rate climbs excessively upon standing, and causes fatigue as well.
Digestive problems are also common in many forms of Dysautonomia, which could account for some of the stomach pain you're experiencing. Not only that, but nausea can be a symptom of low blood pressure, thus a warning to a pending fainting episode. You may want to visit a Gastrointestinal Specialist to check for Gastroparesis (Delayed Gastric Emptying), and other digestive problems. IBS (Irritable Bowel Syndrome) is also common in Dysautonomia.
Autonomic Dysfunction & Dysautonomia Index:
http://www.medhelp.org/health_pages/Neurological-Disorders/Autonomic-Dysfunction--Dysautonomia-Index-Page/show/857?cid=196