I still object to this, personally.
I suffer from PTSD, and I bristle because I've seen too many people on RP boards and other places who have given the affect to characters to add pity depth. It's a very frustrating thing to endure, to watch someone draw a caricature of someone's suffering. Now, I understand that fiction is a reflection of reality, and is our way of coping with it to some degree when it's matters of tragedy... but PTSD is just the latest 'crazy' that people have decided to start using.
It's very much in vogue right now, and is no different from how people would make a cartoon out of autism, or various forms of schizophrenia. I minded those on principle, but the PTSD rings a personal note.
I can echo what these people are saying; you can continue to do work in spite of your PTSD if you either don't suffer strongly from it, or if you are receiving rather constant therapy. It is incredibly unlikely, however, that any form of PTSD, no matter how much psychological rehabilitation you are enduring, will inspire you to take the fight to the streets if you never did before. If your response to watching your wife and children get mowed down before your eyes (Punisher) leads you to start a war on all crime, you don't have PTSD; you are a sociopath who has a vendetta and is refusing to let themselves properly grieve. It's not the same thing. Yes, he has memories that haunt him some, but we all do. They're called regrets and bad memories.
It's a far cry from night terrors, waking hallucinations, overwhelming flashbacks and more. It would not motivate you to fight crime. It would, more often, motivate you to lose your job, alienate your friends and loved ones, drop out of school, and hide in your house, where you can control the stimuli. Well, that's far more likely than making you enact active vendettas, anyway, since it happens all of the time and the other one doesn't.
Yes, however; if you are just a character who's questioning "Do I have PTSD?", I guess you're fine to do this and follow the Punisher example. Just be aware the answer is "No."