@Darcy, I think the main difference between a flashback and a memory is that a flashback neurologically mimics the event as if it was happening right now, instead of it being a recall of something in the past. Also they tend to be involuntary, and perhaps triggered buy something which matches part of the neurological pattern of the original event, but may be unconnected. One I've read about is a flashback to a nightime car accident triggered by dappled sunlight (sunspots) because the person's brain connected spots of light with car headlights coming towards them.
If I stop to think about it, I can build up a pretty accurate composite memory of car headlights at night. Spotting them in the distance, seeing them light up the trees beside the road, the painful dazzle when someone doesn't switch to low beam soon enough. But for someone having a flashback to a road accident, the flashback is as completely out of the blue as the original event, and all the emotions of the event are playing through again, as well as the sounds, sights, smells and sensations of the original. It's like your brain has suddenly teleported you back to the instant of the event, and then out again, and you have to try to mentally readjust to the real here and now.
(Is a bit currrent for me. Older Daughter rang last night having had a flashback to a school bullying incident, and wanting help getting "grounded" again.)
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