> I've had two migraines, one in junior high and one in college. They both just came on suddenly (the one in junior high I had spots in front of my eyes for about an hour before the actual onset, but at the time I didn't know that was a symptom of an oncoming migraine, so the actual headache part was still "without warning" to me.)

The spots you saw are called an "aura" and are one symptom of migraines. A class I took talked about these and I learned that a migraine might or might not include auras and that it was possible to have a migraine that had auras but no headache (which seemed wrong). For some people, the aura could be spots or lines and for others it could be a complete block of certain areas in the field of vision that could grow or move.

Fer"The quack is in"rick