A friend describes brief periods of blindness which begin with a gradual fading of his visual field to black. The entire episodes usually last only 30 seconds or so. Sometimes he faints but usually not. He may close his eyes and stand still for a moment til it passes. This never happens when he is sitting, only when standing. There is no pain ,or dizziness. The only warning is the fading out. He is 21 and has had these mysterious spells since he was 14.