For anyone who really wants to understand cold water survival and the physiology behind it, get yourself a copy of "Essentials of Sea Survival". Even Doug considers this book "a must read for anyone interested in the subject of water survival". I would go so far as to add that it is essential info for landlubbers as well (like me!) because when you really understand the physiology, it will inform your survival knowledge when on land in tough conditions.

Unfortunately the paper book is very expensive now; I suppose it has gone out of print. However the Kindle version is quite reasonable at about $15.