"...If I get bit by a snake am I supposed to just shoot myself in the head to make my death easier..."

From what I have read (and please don't ask for a link or anything, I can't provide one, at least not right now), it is easily possible to survive the average snakebite without much of anything in the way of medical care. You would experience some (or lots) of pain, swelling, lightheadness, and possible loss of mobility of the limb bitten, but you would survive. So I would hold off on that headshot 'til the last minute...