As a medical professional with expertise in respiratory health, I can explain why restlessness is considered an early sign of hypoxia. Hypoxia refers to a condition where the body or a region of the body is deprived of adequate oxygen supply at the tissue level. When oxygen levels in the blood drop, the body responds by increasing the respiratory rate and heart rate in an attempt to deliver more oxygen to the tissues. This physiological response can lead to feelings of anxiety and restlessness as the body is trying to compensate for the lack of oxygen. Restlessness is a sign of hypoxia because it is a manifestation of the body's attempt to increase oxygen intake. The brain is particularly sensitive to oxygen levels, and even slight decreases can cause noticeable changes in behavior and mental status. As hypoxia progresses, if it is not corrected, more severe symptoms such as hypotension (low blood pressure) and cyanosis (bluish discoloration of the skin and mucous membranes) can develop. read more >>

Early signs of hypoxia are anxiety, confusion, and restlessness; if hypoxia is not corrected, hypotension will develop. ... Late signs of hypoxia include bluish discoloration of the skin and mucous membranes, where vasoconstriction of the peripheral blood vessels or decreased hemoglobin causes cyanosis.read more >>