I've said some version of this line to nearly every client I've coached: your nervous system doesn't know the difference between a deadline and a tiger. It's not original to me, I've heard it in different forms for years, but I keep using it because it holds up.
The body has a set of responses built for physical danger. Heart rate up, breath shallow and quick, attention narrowed onto the threat in front of you. Those responses evolved for situations where the danger was immediate and usually resolved one way or another within minutes.
Modern pressure doesn't work that way. A deadline doesn't chase you and then either catch you or not. It sits there for days, sometimes weeks, and in my experience the body still tries to respond to it the way it would respond to something chasing it, because that's the toolkit it has. The result is a stress response with nowhere to discharge and no clear endpoint.
I want to be careful here, because I think this idea gets used lazily sometimes, as an excuse to treat every uncomfortable feeling as a misfiring nervous system rather than an honest response to something that actually deserves attention. Not all stress is a false alarm. Sometimes the deadline really does matter, and the discomfort is appropriate. The point isn't that the response is wrong. It's that the body doesn't have a separate setting for prolonged, non-physical, ongoing pressure.
What I've found useful, in my own life and with clients, isn't trying to talk the nervous system out of responding. It's giving it something closer to what it's actually asking for. A short walk after a hard conversation instead of sitting frozen at a desk. A few minutes of slower breathing before opening the inbox instead of after. Small, physical, unglamorous things that let the body finish something it started.
I don't think there's a fixed technique that works the same way for everyone, and I'd be skeptical of anyone who tells you there is. What I coach is closer to a habit of checking in, noticing when the body is bracing for something that isn't actually a tiger, and giving it a way to stand down that doesn't depend on the external situation resolving first.
I still get this wrong regularly. I've sat through entire afternoons keyed up about something that, looking back, didn't warrant it, and I didn't notice until much later that my body had been in that state the whole time. Recognizing it sooner is a practice, not a switch you flip once and keep.
None of this is about blaming the nervous system for doing its job. It's built to protect you, and it's doing exactly what it was built to do, even when the danger is a calendar notification rather than a predator. The work is learning to meet it there, rather than expecting it to already know the difference.