the panic shock you are referring to is instinctual. it is referred to as the fight/flight/flee/freeze response and it is a physiological response triggered by the brain. your heart beats faster to pump more blood to your limbs so you can run away/fight danger. your system recognizes something as a threat to your well being and triggers this response. it is automatic. all your body's energy goes into saving you.

it is much different than worry which is thought/emotion