When you are stressed, your body prepares for action: heart rate rises, breathing becomes shallow, and muscles tighten. The fastest way to shift that state is to change the breath.
Start with a longer exhale
Inhale through the nose for four counts, exhale for six. The longer exhale is the key because it signals safety.
Do this for two minutes. You are not trying to empty your mind; you are just creating a stable rhythm.
Make it simple
If counting is annoying, use a visual anchor: watch your shoulders rise and fall slowly. The goal is gentle, not forced.
Breathing practices work best as a skill you train on normal days. Then, when you need it, it is familiar.
As with any health advice, if you have medical conditions, adapt with professional guidance.