For 99% of the time the human race has existed we lived in a Stone Age existence where ‘harm’ was obvious and physical. Over the last 15,000 years man has not elvolved but society has evolved out of all proportion.
Unfortunatly, our nervous system (controlled by the unconscious) is still hard wired to protect us from sabre-toothed tigers, not modern stresses.
If any aspect of modern life is viewed by the unconscious as stressful it treats it like a threat (the tiger) and the fight or flight response is triggered to get you away from it. So, for example, going to pieces in an interview is actually the struggle between your unconscious mind trying to get you away from that situation and your conscious mind fighting to stay put.
When the fight or flight response is triggered your body is flooded with hormones that perform certain functions, like increasing respiration, body temperature and moving blood away from any area of the body that isn’t involved in fighting for survival. That accounts for the butterflies in the stomach feeling.
It also takes blood from the brain because you don’t need to think to fight or run away. So you can basically think or feel, but we cannot do both at the same time. The moment the feeling of anxiety or nervousness reaches a certain level you become physically less able to think and this is called an emotional highjack – that is why your mind goes blank and you struggle to put together a sentence. But boy could you outrun a tiger!