Being able to breathe calmly and remain in a state of relative physical relaxation, even while recalling painful and horrific memories, is an essential skill for recovery.
If you consciously breathe in and out slowly and deeply a few times, you will notice the effect of the parasympathetic brake on your arousal. The more you focus your attention on your breathing, the more it will benefit your state of mind, especially if you concentrate to the end of the exhalation and then wait a moment before breathing in again.
As you continue to breathe and notice how the air goes in and out of your lungs, you might think about the role oxygen plays in sustaining your body and how it feeds all your tissues with the energy you need to truly feel alive.