Having done the North Sea survival course (many moons ago) I would recommend it to anybody who thinks they don't need a survival suit in our (UK) coastal waters. The level of disorientation experienced when you go upside down and submerged has to be experienced to be believed. The cold that seeps into your bones very quickly (summer or winter) that dulls your reactions and thinking also has to be experienced to appreciate how quickly you are reduced to an automaton.