What is a common sign of heat-related illness?

Fatigue or weakness is a common sign of heat-related illness because as the body becomes overwhelmed by heat, it can lead to an inability to regulate temperature effectively. This often results in muscle fatigue, weakness, and an overall sense of exhaustion. These symptoms arise as the body depletes its energy reserves while attempting to cool itself, which can manifest as significant physical and mental fatigue.

In contrast, while increased thirst can occur due to dehydration, it may not always be one of the most immediate or notable signs as individuals in distress might not always recognize this need. Severe headache can also signal heat-related issues but is typically associated with more advanced stages or of heat illness, rather than serving as an initial symptom. Increased sense of urgency doesn't specifically relate to heat-related ailments; it could represent anxiety or another stress response rather than a clear indicator of heat exhaustion or heat stroke.