What symptom might indicate the onset of a heat-related illness in a lifeguard?

Altered mental status is a critical symptom that may indicate the onset of a heat-related illness. When the body overheats, it can affect brain function, leading to confusion, disorientation, or even fainting. Heat-related illnesses, such as heat exhaustion or heat stroke, can impair cognitive abilities and decision-making, which are crucial for a lifeguard's responsibilities. Quick recognition and intervention are vital to prevent the condition from worsening, so understanding this symptom can be life-saving.

Chills and shivering are typically associated with a drop in body temperature, often linked to cold exposure or conditions such as hypothermia, rather than heat-related illnesses. Rapid breathing might occur in response to various conditions, but it is not as specific an indicator of heat illness as altered mental status. Excessive fatigue can be a general symptom of many conditions, including overexertion, but it does not specifically signal the acute effects of heat on the body as effectively as the changes in mental status.