I've heard of vipassana, yes.
Yes, I've also had similar experience, in nature, simply observing and letting go.
For me, the acute trauma related to PTSD is fairly recent, making it more difficult in many ways.
But, I've also got a process for that. It works at least 90% of the time to detect onset and walk-back-down the fight/flight/freeze response. It's sort of like a muscle though, my techniques aren't really stand alone strategies, it's..more of a shift in paradigm. I can't guarantee it would work as well for someone else, as it does require a high degree of awareness. A lot of that has to do with being connected to the heart and spirit. I can't personally take credit for what I've discovered.

Thanks for sharing your experience with me @nuthman.

Here's to mutual healing.