Where does one draw the line between having a minor inconvenience and the beginning of a survival situation?
When things start going wrong, on a lonely highway or in the woods, in the city, etc; I start re-evaluating my situation about every 1 hour. When I have decided that I am going to be stuck out in the boonies for the night, I go into survival mode.
"Survival Mode" is to look around and make plans for an expedient shelter, fire, water, and food. My first goal is to get through the night with the time that remains before it gets dark. When I get up the next morning, I am working on a distress signal, improvements to my shelter, getting firewood together for the next night, and addressing further food & water issues.
I will stay in survival mode until I get rescued. This basic outline does allow for cold weather but not snow covered weather and applies to most situations that could happen to myselff here in the swamplands of Lousy-anna and through most of the south.

Again, how do you know when to switch to survival mode?