An action plan is a good idea! :) I haven't even thought of it like that before, but I think that is something I have subconsciously done for myself. I think my "plan" came about naturally, in that my instinctive response when triggered is to flee the situation, and that works out perfectly as I find myself isolated in my room, a bathroom, or a similarly quiet space where I can let the emotions run their course.
I have not found anything (grounding skills, techniques, coping skills, etc) that helps lessen, control, or stop a reaction once it has hit. All of my trigger responses follow a fairly set pattern, with or without the time gap:
1. Boost in adrenaline - bodily reaction / immediate fear response, tightness of chest, faster breathing, tensed muscles, etc. My instincts are preparing me to flee.
2. Voluntary isolation - whether immediately or after some time, consciously or sub-consciously, I ultimately find myself seeking isolation, keeping everything bottled up until I am somewhere alone and "safe" to let go.
3. Emotion overload - anger, fear, confusion, anxiety, etc. Panic attack, break down in tears, etc.
I've never thought to break it down like this, but now that I'm looking at it, pretty much all of my issues/symptoms are somewhere tied into this pattern. Insomnia - when I am isolated but still keeping everything bottled in and don't feel safe enough to relax. Headaches - adrenaline response over a period of time as I'm unable to isolate. Dissociating/withdrawing socially - mentally isolating when I cannot do so physically.
My personal breakdown in this process (the area I have difficulty in) is step three - the emotional overload. At first, the emotional overload was happening all the time, in sync with the immediate bodily response and my attempts to isolate myself and I was like a touchy, misfiring cannon going off in all directions. Now, I get stuck finding myself unable to relax enough or feel safe enough to let the emotional overload run its course....
Anyway, I digress. I may be wrong, but I do not think it is possible to make our reactions to our triggers stop completely, and I think that it is actually important to allow our reactions to take place and run their course. Letting ourselves feel and experience the emotions can get them out of our "system" and make them less "intense" the second time around. It is allowing the response to happen that eventually causes it to fade.
See - the response is happening for a reason. Because of the trauma we experienced, our instincts have classified certain things reminiscent of the trauma as "life-threatening". Say the trauma was a near fatal car accident involving a head-on collision with a red pickup truck. Now, our instincts kick in whenever we see the color red, because (according to our instincts) red is now life-threatening. The emotional response to something classified as life-threatening is immediate and intense, our mind and body screaming at us to take whatever action necessary to preserve our life.
To lessen that response, we have to allow those emotions to run their course in a safe setting. This re-teaches the instincts - "Hey, if red is so life-threatening, then how come I was able to sit next to this person wearing a red t-shirt and nothing happened?" The next time around, the response is a bit smaller, and a bit smaller, until our instincts no longer consider red life-threatening. Now it is only "dangerous". The emotional response for that is smaller, less intense, but can still be stressful and exhausting. Continued exposure can eventually bring it down to "not necessarily dangerous... right now, but should be observed with caution", kinda like how we might treat a hot stove.
Even there though, the response is not entirely gone, and I don't think it will ever be "gone". We will always remember our trauma and our instincts will always remind us of things that could potentially be a danger, but that is how we keep ourselves safe from repeat harms. They key is exposure to the triggers where nothing happens. This makes the trigger less threatening and our responses less intense.
For reading, I'd suggest looking up papers on exposure therapy, desensitization, flooding, and treatment for phobias. Just a quick search now - anxietycoach.com is a good source.