Finals are over and you go out with friends to celebrate. One of your friends has an outdoor hot tub, so everyone gathers there for a warm soak and some beer. After several beers and much laughter about the absurdity of Dr. Watson's human physiology questions, you realize you have to void (pee) and jump out of the tub to go to the bathroom. As your feet hit the deck you feel lightheaded, but make it to the bathroom and back without further problems. After another hour in the hot tub, you all decide to act like Scandinavians and jump into the adjoining lake, which only has a very, very thin crust of ice. Although cold, you feel refreshed and happy about this perfect end to the semester. What happens to fluid volume? Cardiovascular adjustments? Temperature regulation?