Tilly, I also have aura migraines from time to time (though not for some time thankfully). I found that if I sat quietly and tried to relax they would dissipate eventually, though I still had a slightly ‘sensitive’ head for a while. At least by doing that they don’t progress for me to full-blown migraines (with the dreadful headache and numbness I experienced in my late teens). I have no idea if magnesium works, though it would be worth trying if there is any evidence it does.