Immersion Syndrome, also known as Post Immersion Collapse. Particularly common phenomenan during aquatic rescues during the World Wars. The casualty would be in the sea and fine apparantly fine (perhaps a tad chilly!) and by the time they had been winched up into the helo/boat, they had lost consciousness and usually lost effective circulation as well. It's caused by hydrostatic pressure - literally the weight of the sea around you squeezing the fluid from your body (kind of like the special G-Force trousers that jet pilots wear). Whilst you are in the sea you are fine, however, as soon as you leave the water, your blood pressure plumments and you loose consciousness. The best way to avoid this is by taking the casualty out of the water horizontally (or as horizontal as possible). Frank Golden and Michael Tipton (both world-leading Naval Researchers) have done a tremendous amount of research on this subject, and has written a fascinating book which discusses it (and more) in detail - Essentials of Sea Survival. A more minor example is seen in people who train for long periods in the swimming pool. After an hour or more of swimming, you will be bursting for the toilet - literally your body fluids being squeezed out of you! Not that I am a lifeboat crew member (my eyesight is too poor), but the RNLI boys and girls are the best in the world!