If our body temperature falls much below 35°C, the control centre in the brain stops working. The result is that we can no longer control our body temperature: the metabolic rate falls and the body temperature gets lower and lower. Eventually we go into a coma. This is called hypothermia, and if no action is taken the person will die.

Hypothermia

• Symptoms:
  
  1. Low body core temperature.
     
  2. Persistent shivering.
     
  3. Blue lips and/or fingernails.
     
  4. Speech slowed and slurred.
     
  5. Memory lapses.
     
  6. Unconsciousness.
     

• Treatment:
  
  1. Move victim to warm environment.
     
  2. Remove wet clothing.
     
  3. Rewarm victim with blankets or body-to-body contact in a sleeping bag.
     
  4. If victim is conscious, give warm (not hot) fluids.
     
  5. Keep victim warm and quiet.
     
  6. Do not give victim any alcohol, which is a blood-thinning agent, or caffeine, which is a diuretic.
     
  7. Contact medical professionals as soon as possible, if required.

From US Navy boot camp training.