Many people are pursued by fear of blood because of what in their life there are certain difficulties. If suddenly there is a situation in which just it will be necessary, for example, to tie up a wound, and the person faints from a type of blood, then is a problem. Whether it is worth saying that to the person who is afraid of blood to be a doctor any more never.
Fear to fly by plane is observed at the whole 15% of passengers, such fear "aero phobia" is called. Even the fact that the plane is the safest type of transport cannot convince those who suffer from such phobia.