I don't know how quickly this can work for others but the practice has helped me not begin to get activated into flight or freeze: meditate on this idea, I am not the suffering. I am not the body. (In addition to all that Thomas Zimmerman is saying here.) To have a variety of tools available at hand can serve.

Do you do EMDR for clients? Would love to book a consultation with you.

I would prefer deep abdominal breathing. It is hard to deal with flashback by visualizing. Everyone has to find their own method. Good therapist would help building client's own resilience. Unfortunately EMDR is full of this kind of visual "techniques" that only pretend.