The short answer
If you only remember one thing: make the breath slower and comfortable. You can try inhaling for about 4 seconds and exhaling for about 6, but do not force the count. The useful test is whether your body feels a little less activated after a minute or two.
Breathing changes respiratory rhythm and interacts with cardiovascular and autonomic processes. Heart rate commonly rises a little during inhalation and falls during exhalation. Slowing the overall rhythm can change those patterns and may help some people feel more settled without requiring a dramatic claim about “activating” one nerve.
Three techniques worth knowing
1. Extended exhale (4-6 breathing). A simple option: in for four, out for six. No breath-holding, nothing complicated to memorize. If the count feels strained, shorten it.
2. The physiological sigh. Two inhales through the nose (a normal breath, then a short second sip to top off the lungs), followed by a long, slow exhale through the mouth. Even one or two of these can take the edge off a spike of stress. It's the pattern your body already does naturally when you sob or settle down after crying.
3. Cyclic sighing. The physiological sigh, repeated for about five minutes. In controlled research comparing breathwork styles, a few minutes of this daily improved mood and lowered resting breathing rate more than equivalent time spent in mindfulness meditation — a striking result for something so simple.
What breathing can and can't do
Slow breathing can change respiratory rhythm and short-term arousal, and many people find it useful for bodily signs of stress such as fast, shallow breathing or feeling keyed up. What it isn't is a cure for an anxiety disorder. If anxiety is regularly interfering with your life, breathing techniques are a genuinely useful tool alongside professional support, not a replacement for it.
Why "just calm down" never works — but this does
Telling an anxious brain to relax is useless because the feeling isn't coming from your thoughts first; it's often coming from your body. Breathing gives you one voluntary input you can change immediately. A slower, easier rhythm can give attention a physical anchor while the rest of the system catches up.