The thermometer outside your front door doesn't have to register below freezing for winter weather to threaten your health. Hypothermia, a mild to severe drop in the body's core temperature, can easily be prevented. Just knowing the weather forecast and preparing for the cold by dressing appropriately can literally mean the difference between life and death.
Severe hypothermia requires emergency medical intervention.
However, any amount of body cooling needs to be taken seriously and treated with caution and care. Move to a warm, sheltered area. In cases of very mild hypothermia, a warm bath can help restore body temperature. Remove any wet clothes and replace with dry clothes or blankets. Keep the head covered.