The International Maritime Organization, IMO, has just released a revised guide to cold water survival. You can download MSC.1/Circ.1185Rev.1 which is intended to be used by “seafarers” providing “information which will help you if you are unlucky enough to fall into cold water”. Put in plain English, this is something all of us should read and understand. I particularly like Section 9 which deals with the “apparently dead” although in a serious note this is the first time I have seen this subject handled in a succinct way.
The document is a 14 page PDF about 200kb in size.