So sounds like parking lots are maybe a thing for ya, dog.
Personally, when I can't figure out why the f*ck I'm suddenly going all sideways, it's usually an anniversary. Snort. Shoulda seen me last 10Nov. Or not. Not would be better. But it really can be subtle as hell, and act like a brick to the face. Lol. Or it can be about as subtle as a brick to the face & I'll just be sitting there clueless (What hit me???) Oh. Hey dumbf*ck. Maybe you shouldn't <insert really obvious stressor here>.
Figuring out what your triggers & stressors are gives you mad control. Not in the beginning, and it won't feel like it straight out, but once you can identify them? You can start f*cking with them. Chipping away at them. Working around them. Not avoiding them, usually, unless you are about stressed the f*ck out... But by training your brain to stop going no holds barred.
One of my stressors is transitions. Going all Tigger and bouncing in and out of situations & places is something I can do when I'm doing well. I can count on my mind to assess & dismiss or assess & alert as needed. When I'm not doing well? Pfft. I literally need to stop, light a smoke/ tie my shoe/ pull out my camera... something that gives me an excuse to stay put for a minute and scan the damn area completely. If I don't? It lights every damn thing up like Christmas. Not. Useful. Since my instincts have jacked themselves into a live wire & can't sort shit, I have to do it cognitively. Which gives me a headache. But it also starts retraining my instincts again, (all FNG jumping at every little thing... To knowing what actually looks weird), as well as gives me time to back my shit down. Drop my breath rate, drop my heart rate, see clearly. Then I can shift gears from place to place. It gets faster again, over time. Faster & right which is the important bit. But when I'm doing badly? Gotta slow it all down.