Taking your time
I often find myself, when in distress, having a much more heightened sense of emotions and thoughts. They can whirl around at speeds unknown to man, thus making everything seem much worse than it is in reality, and if I was in a good mental health state.
To help calm myself, I've learned to just take my time. It's as simple as that.
Rather than turn to a harmful behaviour, which may feel good for a few seconds but in the long-run makes it all worse, I find something to do; like hoovering, doing the dishes, or bringing the dog for a walk. I ensure that it is done slowly, mindfully and without stress of any kind.
I take my time, and in turn my body and mind slow down enough to come back to the real world, leaving me in a position whereby I forget what I was so distressed about in the first place.