Mine seem to also be over-tiredness and stress related, I don't get the visual aura but do get about an hour's warning from suddenly becoming very restless, jittery and often quite irritable. Darkened room and sleep plus painkillers is usually the only thing that works, DH made the mistake of flipping the light on one day when I had one just after we got together - resulted in him being snarled at to turn it off and me curled in a ball wimpering from the pain...