What stress does to your body

When your brain decides something matters, whether it's a meeting, an argument or a near miss on the road, it switches on the sympathetic nervous system. Adrenaline is released. Your heart beats faster and harder, you breathe more quickly, blood moves to your muscles, digestion slows, and your attention narrows onto the problem.

This is often called fight or flight, but it fires for far more than danger: a first date, a deadline, a crowded room. In a panic attack, the same system goes off at full strength with no danger at all, which is why panic can feel like a heart attack.

• A pounding heart
• Fast, shallow breathing, or feeling you can't get a full breath
• A tight chest, shoulders or jaw
• Butterflies or a churning stomach
• Sweaty hands
• Trouble thinking about anything else

A second branch, the parasympathetic nervous system, works the other way: it slows the heart and settles the body once the moment has passed. You can't switch it on by deciding to, but your breath gives you a way in. Breathing in speeds the heart up slightly, and breathing out slows it down, so long, slow breaths out tilt you toward calm. That's the idea behind the physiological sigh, the next lesson.

A racing heart feels much the same whether you're terrified or thrilled. What differs is how you read it. People who are told before a stressful task that a racing heart is their body getting ready to perform show healthier heart and blood-vessel responses than people who aren't. And people who say "I'm excited" before singing or speaking in public do better than people who tell themselves to calm down.

Calming down isn't always possible in the moment. Reading the arousal as fuel often is.

Before giving a toast, Nia's heart is pounding and her hands are shaking. What's most accurate?