Pretraumatic Stress Disorder?

Please tell me what I don’t understand here. I just have to have missed something. I reread this article several times, too.

Soldiers

According to a German report about posttraumatic stress disorder, about one fifth of German soldiers suffer from psychische Vorerkrankung (pre-existing psychic strain) BEFORE they are deployed abroad.

I mean, I know Germans are super efficient and all that. But how the hell do you get posttraumatic stress disorder before you ever even make it to the post?

Laut einer Studie zu posttraumatischen Belastungsstörungen (PTBS) haben 20 Prozent der Soldaten eine psychische Vorerkrankung. So ist ihr Risiko größer, nach der Rückkehr unter Problemen zu leiden.