What is the most common symptom of hypoxia?

The most common symptom of hypoxia is headache. Hypoxia occurs when there is insufficient oxygen available to the body's tissues, particularly in the brain. One of the first responses to reduced oxygen levels is a headache, as the brain becomes sensitive to changes in oxygenation.

Headaches occur due to the dilation of blood vessels in the brain and are often accompanied by other symptoms as the condition progresses. While confusion, drowsiness, and nausea can be associated with hypoxia, they often develop as oxygen deprivation continues. Therefore, a headache tends to be a more immediate and identifiable sign that the body is experiencing lower oxygen levels, making it the most recognized symptom to watch for during flight. Recognizing this symptom early is crucial for pilots to understand, as it can indicate that corrective action, such as descending to a lower altitude, is needed to restore sufficient oxygen levels.