Reacting to everything as a threat

I had a wonderful coaching session yesterday that revealed my brain is treating so many actually non-threatening circumstances as threats. It’s helped me understand why I’m always so physically tired even when I get enough sleep and why I have the sense that my body is flooded with cortisol so often. My question is how to build a thought ladder from “this is not a threat” to something more positive. For example:

Unintentional model
C: Client emails to ask “when can we chat about these documents”
T: I’m not doing a good job because he must think that I should have already had time to talk with him about the documents.
F: Anxiety
A: Thoughts spin, Worry, Delay writing back
R: I’m not doing the job as well as I want, possible cortisol spike, treating a relatively innocuous email as a threat

Intentional Model:
C: same
T: I’m glad he values my advice and this is not a threat
F: Calm
A: Write back and schedule at time to talk
R: No cortisol spike, retrain my brain to not see requests/invitations/questions as threats, do my job calmly and well

I’d love any advice on how to retrain my brain around this. Thanks!