The only adverse effect is on dark adaptation. Respiration may increase in depth or slightly in rate, and the pulse rate, the systolic blood pressure, the rate of circulation, and the cardiac output increases. 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.