What is the top symptom of dehydration?

Fatigue is often regarded as a primary symptom of dehydration because it reflects the body's reduced ability to perform normally due to a lack of adequate fluids. When the body is dehydrated, it cannot maintain its usual level of function, leading to a decrease in energy and increased lethargy. This symptom is particularly relevant in aviation, where maintaining alertness and cognitive function is crucial for safe operations.

While other symptoms such as headaches, nausea, and dizziness can also indicate dehydration, fatigue is a broader and more generalized symptom, signaling that the body is struggling to maintain homeostasis and energy levels. This makes it particularly important to recognize and address dehydration promptly to avoid further complications, especially in high-stress environments like aviation.