Many an injured hunter has died needlessly in the wilderness simply because he/she was left lying on their back while someone went for help.  In most cases, the casualty became unconscious and their relaxed tongue fell back and blocked their air passage.  In some cases, the casualty vomited, and because they were on their back and unable to help themselves, they got some of the vomit into their lungs.  The acid of the vomit caused a fast-acting pneumonia, which killed them quickly.  In other cases, blood from the casualty's nose or mouth collected in the airway and they asphyxiated.
If the casualty's companion had simply placed him on his side and braced them there before going for help, the casualty might not have died.  What a simple thing to make the difference between life and death.

An unconscious person who is place on their side to protect against fluids in their airway is said to be in what we call "The Recovery Position", because in that position the casualty may regain consciousness without danger of suffocation.  It is also called the drainage position because it allows fluids to drain from the mouth and throat without getting into the airway.  Placing an unconscious casualty in this position is one of the most basic parts of first aid.

a.)  You must first prepare to roll the casualty into the recovery/drainage position by first moving any objects that could be a safety hazard.  Then put the arm that is closest to you down by the casualty's side and the other arm over the casualty's chest or on their chin.

b.) Making the roll.. Bend the leg farthest from you support the casualty's head with one hand, grip the clothing at the waist on the far side and roll the casualty gently towards you
c.) Position the leg.. Keep the leg that was bent.. slightly bend over the casualty's body to prevent the casualty from rolling back and rolling on his face.

d.) casualty in final position.. Make sure that the face is NOT face down and that they are able to breath and allow drainage from the mouth to the ground.  Place his upper arm to keep him from rolling on the casualty's  face, place the lower arm along the casualty's back so that he can't roll onto his back.
If the casualty is on snow, you should place a blanket, sleeping bag, hind, or other protection to keep the casualty's face out of the snow and reduce heat loss.

Other casualties have died because they could not get enough air.  Again, simple body position makes a difference.  A person lying down can't breath as well as one sitting up.  This is because when we lie down, our intestines tend to move up and push against the diaphragm, the flat sheetlike muscle that separates our lungs and guts, and helps us to breath.  Lying down keeps the diaphragm from working well, so we get less air into the lungs.  That is why people with breathing problems such as chronic obstructive pulmonary disease (COPD), emphysema, or asthma prefer to sit up.. that is why we put people in a sitting or semi-sitting position whenever they have trouble getting enough air. 

Next:  Special Challenges in the Wilderness