I have had the same experiences for several years. My migraines began in middle school, but the first aura I experienced was as an adult. I was in the hospital on an IV drip of Magnesium Sulfate (to stop preterm labor) when it happen... I couldn't see. It subsided after I was taken of MagSulfate. Two years later, I was driving to work and had an episode exactly the way you described it. It happened regularly from that point on...
Recently, I was diagnosed with an autoimmune antibody that causes clots. I had clots in my lungs and it was suggested that I may have been having TIA's (mild strokes). The research that I have seen suggests that many people with this antibody (antiphospholipid antibody) have these types of headaches. It is assumed that 1 in 5 people with these headaches have this antibody and don't know it. When they put me on blood thinners, the headaches have lessened. They have not gone away completely, but they are fewer and further between.
I am not suggesting that you have this problem, but that is what I found. It is worth a blood test....
I can say that my migraine with aura is absolutely connected to stress. When I am dealing with some serious stresses of life (ie finances) I will have more headaches with aura.
I do saturate myself with vitamins and minerals. It does seem to help. I found a great product with extremely high grade omega 3 fatty acids... it seems to help.
I am not glad that you suffer with these type headaches (it is frightening to drive sometimes), but it is so nice to know that we are not alone!
Best of Luck in your quest!