You literally lose brain activity and effectively intelligence/IQ when you get PTSD. You can slowly train your brains with mindfulness, getting in the diffused mode of thinking. The trick is to focus on small victories. Learn different meditation techniques and try them out. You'll get your favourite ones eventually. FWIW, I can highly recommend going to a mindfulness course. Guided with audio, a decent book, and a (hopefully) good teacher you'll have use of it for the rest of your life. An unintended side consequence is that I am now, truly, never bored. I've been afraid to be bored without a mag, without my smartphone, without my bag with me, without my wallet, without my lock pick set, without electronic devices, without my powerball. Mindfulness skills I always have with me though (although I do mostly still prefer guided)

In my case it seems it was more due to cardiovascular problems than to PTSD or 'brain self-harm' if I may say so. But anyway, I do try to have deep slowing moment[1], aiming at stable relaxation. But I'm never sure what to expect from meditation. Give me your favorite books.

[1] a side effect of fubared cardiovascular system is that I had to monitor my breathing and heart a lot so I would naturally have sessions of calm slow breathing exercises.

Mind Illuminated by Culadasa has been recommended here before. It gives a path to advance and helped people with years of experience in meditation to become unstuck.