The body is slow to receive this news. Someone can be sitting in a warm kitchen with the door locked and still be running a heart rate that belongs to a much worse room. Nerves work on a delay of weeks, sometimes years.
Which is why it's worth naming the present one out loud, in detail: the chair, the sound of the boiler, the fact that nothing here is asking anything of you for the next ten minutes. Not an argument. Just a description. Bodies believe descriptions eventually.