I occasionally get a "silent" migraine, with amazing auras and tunnel vision - my doctor gave me the term for that which I have since forgotten. There is no pain.
"Optical Aura" I get them too. They are weird and unnerving and I always expect any second for some piercing migraine to start. It never has, but my body seems to know that they usually go together and triggers gut clenching Pavlovian anticipation which leaves a lingering adrenaline overload long after the sparkling colors are gone.
I only get them a couple of times a year, so it's hard to tie them to any trigger, but I had always thought they seemed to accompany major blood loss (I donate blood regularly) when coupled with some other ingredient like stress or virus.
