Red
Mindfulness meditation concepts have helped me a lot with anxiety / an overactive flight or fight response. There are a ton of guided meditations online and apps that can help you learn. An app. I like is the Insight Timer. John Kabat Zinn also has good publications. Before my injury, I was not the type to be in to meditation, but after giving it 20 min. a day for a few months, now I really believe in it.

The STOP concept is one I use when I recognize my brain going off into OCD/anxiety world. It's an acronym for: Stop what you are doing/thinking, Take a deep breath (or three), Observe what's going on with yourself, Proceed...
It's just a quick way to help calm your brain down in an intense moment.

There are also a lot of deep breathing exercises that can help. Like 4 seconds of deep breath in, 1 second hold, 4 seconds of breath out, 1 second hold, repeat...

See also my post about TRE (Trauma Release Exercise) that has been very helpful. Your nervous system probably has a lot of built up trauma that could be released. If you are having PTSD-like symptoms, EMDR therapy really helped me with that.

But there is a lot you can do yourself at home without therapy. Mindfulness, deep breathing, walks, stretching, etc...
Hope that helps.