The military has a saying "the more you sweat in training, the less you bleed in combat". So you need to keep in best condition possible during times of easy so that when you are in a survival situation you can take it easy when you can and do what you must when you must. Every living non-domestic animal and plant does this, deer, bass, pine, or maple. But, if you are 'caught with your pants down' or sticken by a injury, headache or whatever, the best thing you can do is sleep. Take in plenty of fluids too. You should have some asprin in your pack. Or learn medicinal plants. Also, everyone knows that fire hightens moral. I find that if you have to vomit, dont try to hold it in, unless you have no access to food for awhile.
That generally helps me. <img src="images/graemlins/wink.gif" alt="" />