I have a few strategies for these unpleasant episodes. One is the 4-7-8 breathing: breath in (nose) four seconds, hold seven seconds, breath out (mouth) eight seconds... repeat. This is excellent and no side effects. It requires focus and is not possible in social, work, driving etc. situations.
Another I like is a warm bath and laying back with the water above the ears. Excellent, but not unless you are home (obviously)!
Mindfulness, or scanning I've tried and it's like bringing a squirt gun to a forest fire.
Any techniques that work I would love to hear from this group. One thing we all have that is precious to me is this shared nightmare.