Post-traumatic stress disorder
A failure to file a traumatic memory away as 'over', so the amygdala continues to fire it as a present-tense threat, producing intrusive re-experiencing, hyperarousal and avoidance long after the danger has passed.
First principles
PTSD is a memory-consolidation disorder, not simply a strong emotional reaction
During an overwhelming traumatic event, extreme amygdala activation and stress-hormone surge impair the hippocampus's normal job of contextualising a memory in time and place. Instead of the trauma being encoded as a narrative memory ('this happened to me, in the past'), fragments are stored as raw, decontextualised sensory and emotional traces. Because the memory was never properly filed as 'over', a trigger (a sound, smell or thought resembling the trauma) can reactivate it as though it were happening again in the present, rather than being recalled as something in the past.
Educational content pending clinical review. Not medical advice.