I've never been diagnosed with either TPI or PTSD, but my T believes I probably manifested characteristics of both in the aftermath of what happened to me. It's all hindsight, but I think there is something to it.
From what I understand, TPI is often stress-induced. I was under tremendous stress from being in a new school just a couple of weeks after my CSA experience. I had trouble with other kids...normal stuff like being relatively well-liked at my old school to being a nobody at the new school. While I did have a problem with a couple of other kids, I withdrew behind walls, because I trusted no one. I even pulled away from my parents. I didn't trust anyone. I kept my guard up all the time...and like you said, the apparent threat would pass and I was left wondering why I was so worried.
This coupled with out of control ADHD led to some really impulsive behavior. I know there is a danger of second guessing everything, but to this day I think two other things happened that made things worse.
First, I had a pretty severe concussion from playing football. Second, that same tackle that gave me a concussion also tore the meniscus in my left knee. A week or so later, I had surgery to repair the knee. After anesthesia, I was in a fog for several days. I know that I have no empirical evidence, but I believe the concussion, anesthesia, and ADHD converged after the CSA to make me more paranoid and impulsive. I was nervous...and at times withdrawn. Previously, I was more of an extrovert and a talker. I'd talk to anybody about anything. Add testosterone to the mix, and I was a moody, impulsive teenage boy who didn't take guff from anyone, even though I was afraid of the shadows in my room at night---like a toddler might be.
Here's what happened:
My parents noticed and took me to see a psych. because they thought I wasn't adjusting to the move we just made.I never mentioned the CSA. I played up the move and deflected suspicion away from anything else. The psych. Prescribed Elavil and Ritalin later on.
The Elavil managed to make me impotent...as a teenager! I got off of the stuff and stayed on Ritalin for the ADHD. The reason I mention this is that while my ADHD is under control, I'm less impulsive AND less likely to experience any PTSD-like symptoms--including TPI. I'm not saying I had/have either one, but I do recognize some of the classic traits associated with them.
As I got older and out of college, I stopped taking ADHD meds for a long time since that is a kid's disorder, right? Wrong. As I took on more job responsibilty, the ADHD issues of concentration and impulsiveness came back...and not so coincidentally, so did all of the CSA issues that had been buried. I pulled away and put up walls again until I couldn't do it any longer. That's when I told my wife, joined MS and saw a T about it. The T recognized the ADHD... I started medicating that again. Doing so really helped me focus on work, family, and taking on the CSA.
Sorry to ramble, but that's my take on it.