George's post above is so helpful, and his related post goes along with it:  Who is to say when someone is in trouble?

I especially like this part:
Originally Posted By: George Durkee
I found a guy on the switchbacks. When I first talked to him, he seemed fine -- for about 2 minutes when he started talking about his wife's garage sale on the summit. That's called a clue.

(For those who may not know, Mr. Durkee is a backcountry ranger with Seki -- Sequoia/Kings Canyon National Park.)