Our breathing becomes fast and shallow:
our heart rate increases to pump blood to our muscles - ready for action! Our blood pressure increases ..... we become tense and hypervigilent. Stress hormomes, especially adrenaline - and in the longer term, cortisol - stream through our body and unconsciously we become only concerned with survival NOW. Everything else not required for survival is shut down (depending on the degree of stress): immunity, reproduction, digestion, emotion processing and complex decision making. Thats why we are not logical when we are very stressed, why we can't concentrate or make good decisions, why our tummy's play up - remember the "butterflies" or even nausea (or worse!) before an important exam or speech? We may develop temporary reproductive issues (missed ovulation or erectile dysfunction for example).