You can thank the fight or flight response, an ancient survival mechanism, for any physical manifestations of anxiety you experience. Regardless of their intensity - from mild to extreme - all of them are "normal" reactions to either real or perceived danger.
Many years ago, when our ancestors lived in caves, their continued existence was utterly dependent on how well they read and responded to danger.
Those methods for recognition and response to threat were literally hot-wired into their systems. They have been passed down through generation after generation and underpin the reactions to danger we experience today.
The fight or flight response is automatic and by-passes the rational or conscious mind. We do NOT consciously choose to feel threatened or suffer anxiety. It is an instinctive response, happening unconsciously, of its own accord.
What happens at a physiological level is that once the response is stimulated, a part of the brain called the hypothalamus sets off a series of actions preparing the body for either battle, (facing the danger; that is, fight), or running, (escaping the threat, that is; flight).
Chemicals such as adrenalin, noradrenalin and cortisol are released into the bloodstream and complex patterns of nerve cell firing occur. Our body is put on a state of high alert. Our breathing and heart rate quickens. Our muscles are tightened. We become hyper-vigilant and sensitive and our body's entire focus becomes repelling the threat.
Bodily functions deemed non-essential are slowed down as the energy keeping them in optimum functioning condition is temporarily refocused elsewhere. Because you don’t usually stop to either make a speech or grab something to eat while fighting or running for your life, the systems governing digestion or voice are affected. The degree to which we feel challenged directly corresponds to the loss of functioning we experience. The symptoms range from mild to severe accordingly.
What is important to remember about our fight or flight response, is that it doesn’t have a mind. It is NOT a rational reaction. We do not select the circumstances triggering it into action. It works regardless of the type of threat. In other words it is activated whether the threat is perceived, (only in our minds), or real.
It can work positively allowing ordinary people to become heroes. For example the massive surge of adrenalin and allied stress hormones will enable a mother to lift a car off her injured and trapped child or the fireman to rescue people from a blazing building. Once the danger is passed the body returns to normal.
If you're reading this page because you're afraid of making a speech, these suggestions for overcoming public speaking fear are a good starting point.
And you could sign up for my 7 part "Letting go of Fear" e-course. It's a compilation of all the best strategies I know for exchanging public speaking anxiety for can-do, will-do confidence.
If you're here on behalf of a child, check these self esteem builders. They're speech & drama exercises to boost and sustain confidence suitable from kindergarten upwards.