In case of shock, the pressure in the blood vessels is too low in order to keep the vital body functions in operation. Blood flow and thus oxygen supply to heart, brains and other organs are thus compromised, cells begin to die off.
Causes may be in order: too little blood (by loss), (heart) pump does not work (properly), pipes are blocked.
The victim feels miserable, looks bad, has a pale complexion, is cold and clammy, is thirsty and restless, weak and powerless.
Have victim lie. Legs up (except for heart disorders).
Try to stanch external blood loss. Protect against cold. Not to drink or eat.