I don t tire get dizzy when standing for long periods of time, but I get fatigue when I stand for long periods of time. I ve been told by my family physician that I do not have fibromyalgia and I am not anemic. For example if I had to work a job where you stand and do not sit I would come home and sleep. Or if I have to stand for a long period of time to wash dishes (can only do it if I ve slept very well but I cannot wash dishes on less than eight hours sleep. I may not have an ailment of any type, but I might be missing a particular nutrient in my diet for something. My gut say s it s a diet thing. I suspect that I am glycogen intolerant, but I ve struggling to figure this out for years. It has effected my career as a professional singer.