I am a female 38 years, normal body weight, no periods due to continuous hormonal birth control, and over the past 4 years I feel constantly lightheaded and about to pass out if I do not sit or lie down. I feel the same sitting but not as bad. My blood pressure and heart rate are normal, it doesn't drop when I stand, and blood tests, ECHO and ECG are normal. I am not on any medications to cause this, don't drink or smoke and previously healthy all my life. I drink tons of fluid so I am not dehydrated. I eat a normal diet, not vegetarian.