Final answer:
Chris Legh's collapse was primarily caused by hyponatremia, characterized by dehydration and reduced blood volume that leads to circulatory failure and can cause severe complications like brain damage or death.
Step-by-step explanation:
The primary cause of Chris Legh's collapse was hyponatremia. Hyponatremia is characterized by dehydration, reduced blood pressure, and decreased blood volume which can lead to circulatory failure. This condition might be a result of an imbalance of sodium in one of the body's other fluid compartments, or from a dilution of sodium due to water retention. At the cellular level, hyponatremia results in increased entry of water into cells by osmosis, causing swelling of the cells. This condition can have severe consequences such as brain damage or death when swelling of neurons in the brain occurs.