I posted on a thread about migraines a while back. About 10 years ago I had the onset of a migraine (with aura) while I was driving at night dojng about 80mph in lane 4 of the M25. For those of you who've never experienced "aura" (for me anyway) it starts as a big blind spot in both eyes simultaneously and rapidly turns into a combination of a big blind spot surrounded by very bright constantly flickering lights. The skull splitting headache comes on about 15 mins later and thwe whole thing is over after about 3 hours. It was very frightening....I could barely see where I was going and had to try to get myself across four lanes of high speed traffic on to the hard shoulder. Fortunately my wife was with me and was able to give instructions ("lane three is clear" etc) and drive me home once we'd made it!!
Getting this while flying would be horrendous, and to be honest, the worry about getting one while flying would take the fun out of it a bit I reckon.
Haven't had one for ages (since I stopped eating cheese....)