well.. i just HAD to respond to this one.....

there are a lot of physiologic changes that occur in the body that create PTSD. One thing that happens in a very stressful situation is the amount of hormones in your body (specifically norepinephrine and epinephrine) increase dramtically as part of the 'fight or flight' complex of self-defense/preservation. its a NATURAL thing than happens in every animal on God's green earth.

blood in the extremities (arms/legs) is squeezed back so the organs and brain have enough oxygen and blood in order to respond to physical and mental stress.

other things happen - your kidneys almost completey stop making urine to stay hydrated. all food digestion nearly ceases. heart rate increases causing increased cardiac oxygen consumption and increase breathing effort. this is only the start and things increase as the stress levels increase.

simultaneously the vagus nerve which travels along the spine/aorta is sending LOADS of information back to the brain about stressed organs. the increased breathing effort helps calm the vagal nerve with constant massage through the diaphragms breathing motion.

there is a theory that when an individual is subjected to high stress levels that the norepi/epi levels in your brain have a direct role in memory retention related to the significant event. your brain is on overdrive trying to process all that is going on and is EXTREMELY focused in all the little details going on. this is why people who have traumatic experience have such an easy time recalling such small details about their event compared to the individual who is completely relaxed has such little retention about common everyday events.

PTSD can be triggered through similar high stress events that trigger SIMILAR circumstances. i will give this personal example to illustrate:

i was on a mission while deployed to iraq with my platoon to recover a downed civilian helicopter. no survivors were found as the helicopter was shot down with an RPG and crashed on impact. anyone who did live by jumping out was shot and burned. being a medic i was on the detail to recover all the bodies from the crash site as a security perimeter was established.

after the mission, and for some time afterwards, i couldnt go near a barbeque for the smell would put me in severe convulsions, throwing up uncontrollably until the smell was gone. even driving by someplace and having a smell was horrible. it took months for it to go away.

THAT is PTSD in a nutshell. sometimes its a day to day thing. sometimes its not. it all depends on the situation and how it reflects on the person. TBI (traumatic brain injury) can also play a SIGNIFICANT role in a persons behavior and is often confused with PTSD. bomb blasts and other significant forms of consussion makes physical changes in the brain and changes a persons behavior.

i hope this helps.