Haha yeah I bet it hurts like a bitch! The guy doing the ice bath study at my lab had the hydrostatic weighing tank filled with water and ice cubes floating around the top, looked like torture. Body temperature drops fast in cold water, so keep don't keep yourself in there too long. When subjected to extreme cold stress, one of the body's initial responses is shivering, but eventually you'll stop shivering even though your body temperature is still dropping. You'll feel relaxed but it doesn't mean you're safe. I don't think you'll have to worry much about it unless your in there for a long time but be careful regardless.