What condition is caused when a casualty cannot rid themselves of excessive body heat due to a breakdown in sweating?

The condition caused when a casualty cannot rid themselves of excessive body heat due to a breakdown in sweating is heat stroke. Heat stroke occurs when the body's temperature regulation fails and the core body temperature rises to a dangerous level, usually above 104°F (40°C). This state is critical because it can lead to damage to the brain and other internal organs.

During heat stroke, the body stops sweating, which prevents normal cooling processes and can lead to further health complications. Symptoms can include confusion, altered mental state, hot and dry skin, rapid heart rate, and even unconsciousness. It is considered a medical emergency and requires immediate treatment, such as cooling the individual and seeking medical assistance.

The other conditions listed do not signify the same level of severity or involve a complete breakdown of the body's ability to cool itself through sweating. Heat exhaustion is less severe and involves heavy sweating and dehydration, while heat cramps are painful muscle spasms that occur due to loss of electrolytes, and hypothermia is related to abnormally low body temperatures, not excessive heat. Hence, heat stroke is the appropriate answer for this condition.