Yes, it can actually. There is actually such a thing as PTSD w/ psychotic features, which is what I have. I had a psychotic break (A.K.A.- my nervous breakdown) from going through too much stress and trauma. Due to my PTSD, I get more psychosis due to more stress.
Though, yeah- if you go through too much stress on top of the PTSD you're already going through, then it is ABSOLUTELY POSSIBLE to have a psychotic break- although, everyone reacts differently to high stress. I got extremely physically ill as well as psychosis during the nervous breakdown I had (it REALLY sucked :/ ).
But just because you lose touch with reality doesn't necessarily mean you've lost touch for good- it doesn't mean you have schizophrenia! You can regain touch with reality once you become stabilized and learn coping skills. Plus, it also doesn't mean that you will never heal- psychosis is NOT a factor in that decision, trust me. Just try to keep your stress at a minimal level- talk it through with your therapist- and you'll be fine ;) Hang in there! :)