Do not get into your bag cold.
Hot drink before bed, star jumps to warm you up then straight in.
If you get in cold ,you will stay cold.
Hope this helps.
best.
Chris.
In the First Aid for survival training I covered as part of my advanced First Aid, a Hot Drink causes your body to cool down and a cold drink causes the body to heat up, especially if the drink is a glucose / simple sugars mix. The liver is the body's central heating boiler that burns sugars and fats to produce heat, the body has a thermostat that like in a house if it is warm the thermostat clicks off and the boiler ceases to burn fuel where as cooling causes the thermostat to switch on and fuel starts to be burned.
The body is no different, so when out in an environment that is turning cold, put a layer of clothing on before you feel the cold, eat a snack that contains sugars and high calorific and energy sustaining ingredients and you should be fine. Hydration is as important as calorific intake but you can also over hydrate. While headaches and cramp are the obvious lack of hydration, over hydration leads to water intoxication and can result in digestive problems, behavioural changes, brain damage, seizures, or coma. If you have kidney problems then the onset of symptoms of water intoxication will be quicker.
Since the brain is the organ most susceptible to over-hydration, a change in behaviour is usually the first symptom of water intoxication. The patient may become confused, drowsy, or inattentive. Shouting and delirium are common. Other symptoms of over-hydration may include blurred vision, muscle cramps and twitching, paralysis on one side of the body, poor coordination, nausea and vomiting, rapid breathing. An average healthy adult will be able to process fluids without becoming intoxicated but those who have renal problems can and often do exhibit symptoms.
Any trained survivalist will tell you that the first rule of survival, keep dry, is important because if you are dry, you are warm. If your clothing becomes wet, you will become cold and suffer from exposure and your survival rate drops dramatically. This obviously depends on climactic conditions, so in hot countries you should not immediately strip off because you can still suffer from exposure but your first rule is to keep as much of your body clothed and in shade and wear a hat and hydrate at regular intervals with a mix of water and electrolytes to replace what you are losing through sweating and breathing.
So back on track... you can also sweat too much with too many layers and your clothing can become wet and that can cause cooling which is why your body sweats in the first place but in the wrong environment, this can be your enemy, so regulation of your clothing is important too.
Most of your body heat leaves through your legs, they are your body's radiators and second to that is the heat loss through your head, so keeping warm can be as simple as putting a hat on and wearing trousers designed for hill walking (lined).
Like any wilderness adventure, knowing what the local conditions are like and taking appropriate equipment with you is important as no one really wants to become a S & R subject or another statistic like some people do through not taking precautions, planning or leaving instructions on where they are trekking off too.
