Final answer:
When immersed in cold water, a person is primarily at risk of becoming lethargic to conserve heat as part of the body's response to cold, including shivering, reduced blood flow to the extremities, and increased energy breakdown, with potential risks of hypothermia and frostbite.
Step-by-step explanation:
When immersed in cold water, a person is at greatest risk of becoming lethargic to conserve heat. The body reacts to exposure to cold by initiating various physiological processes;
Shivering, which generates heat through random muscle movement.
Increased breakdown of stored energy to produce heat.
Reducing blood circulation to the extremities to maintain the body's core temperature.
Over time, if the body's energy reserves are depleted and core temperature drops significantly, there is a risk that red blood cells will not provide enough oxygen to the brain. This can lead to confusion, lethargy, and eventually loss of consciousness or even death.
Additionally, there might be a risk of frostbite, especially on the fingers and toes, due to reduced blood flow, potentially leading to permanent tissue damage and even gangrene.