Extreme cold has some peculiar effects on the human body. While these have now moved from the realms of folklore into medically accepted phenomena, the underlying causes still have scientists scratching their heads. When a dead, naked body is found in a wardrobe, the doctors know that foul play is unlikely to be involved, but their explanation is rather vague… a sure sign that this is fortean territory.
Hypothermia is the body’s reaction to cold. Vasoconstriction occurs, the diversion of blood away from the extremities to maintain core temperature. As a medical mnemonic has it, the ‘umbles’ set in: the victim starts to stumble, fumble, mumble and grumble. The first two are due to the lack of co-ordination and sensation. The others are due to the effects of hypothermia on the brain, descriptively known as “cold stupid” when the victim increasingly loses the ability to think rationally.
Hypothermia is generally a helpful adaptation to cold, though of course losing dexterity and mental acuity can be hazardous if, say, you are a mountaineer. But there is a more complex adaptation, first documented among Inuit hunters by Sir Thomas Lewis in 1930. He found that vasoconstriction alternates with periods of vasodilatation so that the extremities receive a periodic burst of warmth, enough to restore functioning. This effect is known as the Lewis Hunting Reaction.
If the cold continues for an extended period, something more mysterious happens. After a certain point, the body gives up on vasoconstriction completely. It has been suggested that this is because the muscles that control it become tired, but this has not been proven. When this happens, blood flow is restored to the extremities and victims start to feel warm. So warm that in the mental fuddlement of hypothermia they often start to get undressed.
So-called Paradoxical Undressing is seen in about half of all hypothermia victims, and of these about a third get completely undressed. For reasons not understood, undressing generally starts with the lower half of the body. Clothing may form a trail behind the victim, or may be scattered around them.
Another peculiar feature kicks in at the same time, the Hide and Die syndrome also referred to as “terminal burrowing behaviour”. This happens in about 80 per cent of cases where there is paradoxical undressing. The victim is found in a narrow, enclosed space, typically one which can only be accessed by crawling, such as under a bed or sofa, or inside a cupboard. Previously, investigators might have suspected that this was an attempt to hide the body, but distinct marks on the knees and elbows show that the victims have crawled into these peculiar locations themselves. 
Researchers believe that terminal burrowing is some sort of primitive instinct controlled by the brain-stem, but again this has not been proven. Interestingly, terminal burrowing is most common in cases where there has been a gradual cooling rather than extreme cold. One theory is that it is a survival of an earlier mammalian urge to hibernate, as it corresponds quite closely to other animals’ seeking out enclosed safe places for hibernation.
Terminal burrowing also seems to correspond with another mental state found in victims of hypothermia, in which they go from “cold stupid” to “cold crazy”. Delusions and hallucinations are commonly reported. Sometimes, this takes the form of an out-of-body experience where the victims see themselves from outside.  One hypothermia victim who was found partially undressed said that he “felt like a bug”. When asked to explain what he meant by this “he became agitated and upset”. 
Victims often report that during this phase they have a sensation of warmth and peace. There is a famous literary description of this in Hans Christian Andersen’s 1845 story of the Little Match Girl. Suffering from extreme cold, the girl experiences a series of hallucinations or visions culminating in her being carried to heaven by her grandmother. She is found dead of cold the next morning, with a smile on her face.
(The more dramatic condition known as “Arctic Hysteria” or Pibloktoq does not seem to be related to hypothermia. Although this may also involve running around naked in the snow, it has other features such as depression and screaming which are not associated with hypothermia. It is believed to be related to overdoses of Vitamin A from the livers of arctic fish.)
Perhaps humans have a vestigial hibernation instinct triggered by cold. In 1900, the British Medical Journal noted the practice of Russian peasants of sleeping through the winter. An entire family would gather in one room to sleep, waking briefly once a day to eat a piece of bread. However, to count as true hibernation body core temperature must be significantly lowered. Bears, for example, drop from 37 C (98.6 F) to 31 C (87.8 F).
There are a few instances suggesting that humans, especially children, can survive with lowered body temperature. In one of the most extreme, a 13-month-old girl was found in the snow. The air temperature was –24 C (–11.2 F) and her temperature was down to just 16 C (61 F), but she was successfully revived by the University of Alberta Hospital in Edmonton [FT146:6]. For other cases see FT45:28–29, 131:8.
The possibilities for human hibernation are not yet understood, but they may be important. Researchers believe that an artificially induced hibernation might allow accident patients to survive long enough to be treated. Or perhaps one day we will all be able to sleep through winter.
1 Forensic Pathology Reviews
2 'Five Minutes in the Arctic Ocean', The Week, 6 Aug 2009
3 'A Case Report of Hypothermia in the Wilderness', Wilderness and Environmental Medicine, Vol 13, No. 2