I think some of my migraines have been triggered by neck/shoulder tension, but only when it's gotten rock hard and painful in that area, so you would probably have noticed that before this one hit. You clearly also notice the aura when that signals an onset. I guess sometimes migraines do just come out of nowhere. I'm glad to hear you made it safely off your bike, onto the side of the road, and called for pick-up! That's a feat in itself, given that migraine can leave you vision-impaired and "spacey", so you should feel proud rather than embarrassed. Definitely no reason for embarrassment here! Well done you! Knowing you managed this, you should also feel fairly safe about getting back on the bike (or driving a car, for that matter), in spite of the sudden onset this time. But yeah, if you've got a good doctor, it's probably a good idea to report the episode and ask if that's something (s)he would want you checked out on.