[quantumet]

http://en.wikipedia.org/wiki/Aura_(symptom)

It's a grab bag of weird perceptual effects that can precede migrane attacks (and apparently epileptic seizures), and they can be very disconcerting if you don't know about them.

In my case (only had them once or twice), I experienced the same visual field disassociation as you did (in addition to the scintillating scotoma thing) - I could see individual things in my field of view just fine, but I could not properly combine the whole scene into a whole. Like looking at a cubist artwork - each part is reasonable but the whole doesn't fit together, or had parts missing (not holes, just discontinuities). Of course, very shortly after that started, the migrane headache arrived.

Might want to consider talking to a doctor about it; while AFAIK auras are harmless if a bit scary, if you don't have them associated with a known issue like migrane headaches, might be good to try to find out where they're coming from. Not that anyone really seems to understand the mechanisms involved.

[glaugh]

I get the blindness aura thing just before I have a migraine (which doesn't happen much anymore since I stopped accidentally suffocating myself with my pillow..).

The experience for me is absolutely identical to that of a blind spot optical illusion, except bigger and in a different area (just a bit off from the center). It's not generally obvious that there's an issue, the brain fills it in, but if I put text in that part of my vision I'll notice I can't actually read it.