What is the 5-4-3-2-1 grounding technique and when is it useful?

It is a sensory attention exercise for moments of acute anxiety: name five things you can see, four you can hear, three you can touch, two you can smell and one you can taste. The mechanism is straightforward — it occupies the attentional resources that anxious rumination is using, and it anchors you to present sensory input rather than anticipated threat. It works best for panic and acute spikes, and is not a treatment for underlying anxiety. Practise it when you are calm, because a technique you have never rehearsed rarely surfaces when you actually need it.