What is a common symptom of hypoxia?

Increased breathing rate is a common symptom of hypoxia because the body responds to lower levels of oxygen by attempting to take in more oxygen to meet its needs. This physiological response is a mechanism to compensate for the lack of oxygen in the bloodstream. As oxygen levels drop, the brain signals the respiratory system to increase the breathing rate, allowing for a larger intake of oxygen to improve overall oxygen saturation in the blood.

While the other symptoms mentioned can occur in various conditions, they are not specific indicators of hypoxia. Excessive sweating, for example, can be related to numerous issues including stress or fever, euphoria may be associated with certain conditions and can sometimes occur at higher altitudes but is not a direct result of hypoxia, and freezing sensations might be linked to other physical or neurological problems. Therefore, the increased breathing rate is the most direct and recognizable symptom associated with a low oxygen environment, making it the correct choice.