Like all other animals, human beings have evolved ways to help us protect ourselves from dangerous, life-threatening situations. When you feel under threat your body releases hormones, such as adrenalin and cortisol, which help physically prepare you to either fight the danger or run away from it. These hormones can:
•make you feel more alert, so you can act faster
•make your heart beat faster to carry blood quickly to where it’s needed most

Then when you feel the danger has passed, your body releases other hormones to help your muscles relax, which may cause you to shake.

This is commonly called the ‘fight or flight’ response – it’s something that happens automatically in our bodies, and we have no control over it. In modern society we don’t usually face situations where we need to physically fight or flee from danger, but our biological response to feeling threatened is still the same.