Sometimes people use the abbreviated form, i.e. Post Traumatic Stress, hence the initial PTS, as opposed to the full name of Post Traumatic Stress Syndrome, which is PTSD. Furthermore, dialogues in the series aim for naturalness, so you have to bear in mind, that perhaps not all the characters would give it the full technical term, but that which most civilians would use, i.e. PTS, since Post Traumatic Stress is not exclusive to military personnel.

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