check this out:
http://en.wikipedia.org/wiki/Cortical_spreading_depressionI've read articles that can make a direct correlation between this phenomenon and the aura of a migraine. It's like a wave of electrical activity that begins at one region of the cortex and spreads out over an area, and the blind spot and increasing growing flashing lights thingy that you see is when it's going over your visual cortex.
I get these too, and it fascinates me (not during, of course; I do the same as you, take some Excedrin PM and hit the sack ASAP to sleep through the worst of it, if possible.
One thing I've noticed consistently is that I'm famished when I awake.
Edit: here's a good article, one excerpt:
Various other observations support the idea that cortical spreading depression underlies aura. When recorded by advanced imaging technology, the timing of the depolarizing wave dovetails neatly with descriptions of aura. The electrical wave travels across the cortex at a rate of two to three millimeters a minute, and the visual illusions that accompany aura are exactly those that would arise from an activation spreading across the cortical fields at just that rate. The suite of sensations that aura can entail—visual, sensory, motor—suggest that corresponding areas of the cortex are affected in sequence as the “storm” crosses them. The dark spots that patients experience after the bright hallucinations are consistent with neuronal inhibition in the regions of the visual cortex that have just experienced the hyperexcitability.
http://www.scientificamerican.com/article.cfm?id=why-migraines-strike&page=2