Well, this is a job for one of our medical Flutherers, but basically vasovagal syncope or fainting is not serious and passes quickly. It occurs when a sudden stimulus overloads your nervous system causing a drop in blood pressure resulting in too little blood getting to the brain and loss of consciousness.
Shock is the body’s attempt to deal with serious trauma with loss of blood to the body by taking steps to maintain sufficient blood for the vital organs and brain. It is a cascading response that, if not treated, can result in death.