Maggies Farm points the way to a good site re outdoor survival skills in cold and cool weather. The info is dated and still critically vital… 

“…many hypothermia victims die each year in the process of being rescued. In “rewarming shock,” the constricted capillaries reopen almost all at once, causing a sudden drop in blood pressure. The slightest movement can send a victim’s heart muscle into wild spasms of ventricular fibrillation. In 1980, 16 shipwrecked Danish fishermen were hauled to safety after an hour and a half in the frigid North Sea. They then walked across the deck of the rescue ship, stepped below for a hot drink, and dropped dead, all 16 of them.”   

http://maggiesfarm.anotherdotcom.com/archives/10894-Freezing-to-death.html

http://www.ariverneversleeps.com/fishingwest/outdoors.shtml

Symptoms to look for:
-Intense shivering; slowing of pace, poor coordination, ability to perform complex tasks.
– Shivering persists, stumbling, thickness of speech, sluggish thinking, feeling of deep cold or numbness.
– Shivering decreases. Disorientation. Stiffening of muscles, jerky movements.
– Exhaustion, hallucinations and inability to get up after rest.