I apologize in advance for the length of this post, but this particular subject has been a 'big deal' for me ...
I had an disabling migraine condition from circa age 18 up to about age 30. The condition was sufficiently severe, examined, and documented that it was the primary reason I was rejected for military service on medical grounds. In talking with doctors and lots of other migraine sufferers I came to learn that the degree and 'style' of the preliminary aura phase varies quite a bit among individuals.
For me, there was usually a pre-visual-aura symptom that could easily be overlooked. My attention / concentration / situation awareness would 'side-slip' and I would have a hard time staying focused on the topic or task at hand. There was no sensation of mental fuzziness or loss of acuity per se, but I simply couldn't stay on track. I used to characterize it as 'my consciousness hitting a patch of ice and starting to swerve'. At about the time I recognized this effect I would usually start noticing the visual effects.
It was rare for me to get a good enough look at the individual 'sparklies' to confirm they were uniform geometrical shapes. More commonly (for me) they were numerous discrete glints or flashes that collectively undulated in a pattern reminiscent of sequined ocean waves. Most often these were at the periphery or the very center of my visual field. There were one or two very severe attacks in which these figures filled my visual field.
Other sufferers I met had different experiences. Some had exclusively 'peripheral sparkly' effects, some central, some whole-field, and others mixed-mode like myself. Some described their sparklies as being considerably larger / larger-grained than mine. Some claimed the presence of multiple regular geometrical shape types (whereas I was never sure I saw more than one type).
The classic dancing lights aura, though, was only a minor portion of my pre-pain aura. I would get an outright 'blind spot' on one or the other side - typically the left. If partial, this would be a region in the center of my visual field or the entirety of my visual periphery. Most often, though, the 'blind spot' effect would subsume the entirety of my visual field on the affected side. Onset of the blind spot was usually rapid and all-at-once, but there were occasions when it seemed to begin as a 'partial' and immediately go 'total'.
The blind spot effect is very difficult to describe. You know that most extreme peripheral verge of your visual field, in which you can tell there are objects / colors / forms yet cannot somehow bring them into discrete 'grasp'? Imagine your entire visual field being like that. I could sense there was light / dark and differentiation of the visual field into subsdiary sub-portions, but I was not literally 'seeing' these distinctions. Any attempt to focus on a discrete 'target' I intuited was here or there resulted in nothing differentiable from the muddled background.
In the most severe cases, the affected visual field would be perceived as a muddled grey fog or fluid. Doctors and others would juxtapose the 'pointillism' of the sparkly phenomenon with this blind spot effect and suggest it must be like the grey 'snow' on a television set with no signal. It was never like that - it was always 'continuous' with no 'pointillism'.
This effect was distinct from the 'dancing sparklies', and the two were co-present only when transitioning from one to the other. The 'blind spot effect' only affected one or the other eye - never both at once. It was common for one eye to be 'blind-spotted' and the other functionally normal with 'dancing sparklies'.
These aforementioned effects (in vary degrees and combinations) always preceded any 'somatic' effect (nausea, hot / cold flashes, transient numbness, and of course the splitting head pain). With me it was not unusual for non-head somatic effects to manifest for up to 15 - 30 minutes before the head pain arrived. Even with the entire above-cited progression being played out, my head would 'explode' on a variable timetable ranging from 2 - 3 minutes up to around 30 minutes after the first noticeable symptom.
No specific somatic cause was ever determined, even though I have been examined / tested during actual episodes.
As I said, the migraines became less and less frequent - disappearing altogether in my early 30's.
I occasionally experience a discrete bout of 'sparklies', but no blind spotting and no headaches (or at least no head pain).
Now fast-forward ....
At the age of 48 I began having 'memory attacks' - episodes of extreme confusion, forgetfulness, and cognitive incapacity. I would 'wake up' in the middle of daily activity not knowing what I'd been doing or why I was where I was. I could functionally normally if I could stay focused on a specific point of reference (topic; document; etc.), but once I lost that focus I might as well have just awakened in the situation. I could recognize faces but fail to associate names with them and even fail to recognize acquaintances. These 'attacks' always had a rapid onset and the effects would persist for several hours (but typically not overnight) - just like the earlier migraines.
I've once again been examined / tested / MRI'd, etc., in a vain attempt to figure out what's wrong. Alzheimer's, stroke, tumors, etc., etc., have all been ruled out. Neurological and psychological testing has identified no deficits (in fact I remain well above-average in test performance).
Neither of the two leading medical hypotheses (non-destructive transient ischemic attacks / post-traumatic stress) are convincing enough for doctors to 'commit to them'.
In the course of these more recent attacks I've noted (and reported) that the effect is like an amplified version of the 'consciousness side-slipping' that was my preliminary migraine symptom.
One neurologist told me (circa 2003 - 2004) there was growing recognition for a syndrome then termed 'painless migraine'. It seemed to mainly affect middle-aged and older people who'd been chronic migraine sufferers in youth. The symptoms usually replicated aspects of their younger migraine experiences, with the sole exception of the head pain.
I don't know for sure, but ... My working theory is that the later 'memory attacks' are a manifestation of the same 'pre-visual-aura-cognitive-disruption' I noted back in the Bad Olde Days of my active migraine condition.
Again - sorry for the length ....
