In this stage the physiological compensations do not provide adequate oxygen for the tissues. Hearing is one of the last senses to be impaired or lost. Thinking is slow. Calculations are unreliable. Memory is faulty.
Judgment is poor.
Reaction time is delayed. Over-breathing due to excitement or stress. In the critical stage consciousness is lost. Death follows shortly. An immediate descent below 10,000-feet msl will provide rapid recovery from hypoxia's symptoms.