I had this happen once, and I'm always afraid it will happen again. In my case, I woke up with a migraine, unable to see out of one eye. I didn't recognize a television show that had been on for years when I was younger, and I forgot what numbers and letters looked like. The home phone number I had for 20 years? Couldn't remember it. I was lucky enough to finally press the right numbers, and was told to write something basic, like "hockey". I still have the paper, and it's a bunch of vertical lines. I had no idea where I was, and I'm thankful that I wasn't out at the time. It's a very odd, scary thing to say "What do letters look like? What's an h?" I saw a neurologist right away, and after going through numerous tests, the verdict came in: migraine. I couldn't believe it, I thought for sure I'd had a stroke; all the symptoms were present. I've always suffered from bad migraines, and still do, which isn't reassuring.
Anyway, I'm glad Serene's awful incident has turned out to be the result of a complex migraine and not something far more serious. If I hadn't suffered from something similar myself, I would have found this cause hard to believe. That was pure terror in her eyes, and I'll never be able to watch that video again.
ETA: The worst part is knowing that the situation isn't right, that something's wrong, at the same time this is happening.