1. When something happens that reminds you of an embarrassing, difficult, or so-disturbing-that-you'll-never-be-able-to-unsee
-it event in your life.
2. Actual flashbacks to actual battles. Can happen with PTSD.
Oh my god, that was the same position my parents used when I walked in on them as a kid. I'm having war flashbacks!
Don't you trigger a war flashback, son. I once killed a man!