A flashback to me is something that produces a reaction in my body that is not appropriate to what I'm looking at, hearing, touching, or smelling. For instance, looking at a friendly, happy, non confrontational man wearing Jesus sandals.....I feel terror, panic and actually feel my body wanting to cower down, I've actually disguised the cowering up by saying I'm cold. The Jesus sandals send my mind back to 45 years ago. The man I am looking at has done nothing at all to produce this fear in me. I'm far better now at dealing with these situations, by recognising them.
If I see a bunch of roses in a crystal cut vase it I feel sad, lost and lonely...and smell furniture polish mixed with cooking smells of boiled cabbage. I can only guess where that one comes from, but have a fair idea.