Jungle_re; I think you'd agree that constant awareness of the effects various tasks are having on you; your physical condition; knowing when to take off or add a layer, and when you're going to have to seek shelter before it's a matter of urgency, has to be paramount in cold environments. I've been fortunate enough never to have reached the deeper stages of hypothermia you refer to, but do believe that many variables make up your quota of "luck".
Lisa, what you describe as muscle, tendon and joint pains due to irregularly practiced tasks are, as you know, perfectly normal. I think I can put my hand on my heart and say that I've never seriously trained or practiced for any of my various pastimes, loosely termed "mountaineering", also canoeing and scuba diving, but rather formed a habit of depending on my physical fitness and the routine of turning various shades of purple on the first day out, in the knowledge that I'd be fit as a butcher's dog tomorrow.... a fleeting luxury, as John Fenna will no doubt testify. Sometimes fun hurts!
I've been in a few sticky situations, none of which lasted for more than a few days before fortunately coming to the right decision between the best route and the road to nowhere. Downward spirals, it seems to me, are a combination of events, circumstances and bad decisions. Preparation, a cool head, confidence in ones abilities and a sense of humour are essential in forming the Positive Mental Attitude, John chucked into the equation. Without these elements, PMA can only ever be an unknown quantity to most who have never been in a long term situation, possibly alone and living on your wits to pull you through. Physical fitness is of course an important part of this but, short of a debilitating illness, I'd prefer to rely on my knowledge, common sense and skills.
As Eric Idle would say, "Always look on the bright side of life."
ps; And let's not forget Stuart's post, that "Survival is all about a good cup of tea."
My apologies if I appear to be flippant at times, but as we say up here, sometimes if ye don't laugh ye'll greet!