I often go back in my mind trying to recall the event that initiated at the onset of my HPPD symptoms. I can recall the same event happening both times my HPPD got worse. The first thing that happened before I got HPPD symptoms was seeing flashing of light in my eyes while they were closed. Blue streaks of lightning, like a storm going off under my eyelids and inside my brain. I vaguely recall an uncomfortable sensation of muscle constriction that accompanied this, really kind of felt like I was under a spell of the storm.
Did you have this when your symptoms started? It's medical term is called aura, but I don't recall getting a migraine with my aura visuals.