You never REALLY know whether it's a migraine or a brain tumor (or an aneurysm or stroke). Says she who actually had an MRI last month to be really, really sure (but I've had bad migraines for years and just added the REALLY fun symptom of extreme dizziness before one sets in). I'd gotten used to the flying spots aura (the first time I was sure I was having a stroke, and went to the ER, because I got extreme tunnel vision - I could only see out of one eye and part of the other.
It was loads of fun, btw, being told that you have "normal" white matter changes for a migraine patient. That is, my MRI is NOT normal for a normal person, but it's consistent with a relatively "normal" MRI for a long term migraine sufferer. Oh joy.