Not the same as hyperpnea (tachypnea), as hyperventilation is an increase in ventilation disproportionate to the level of carbon dioxide in a person's system.
In a normal person breathing normally at rest, the breathing center in the brain will regulate PaCO2 (the concentration of CO2 in the blood) to between 35 and 45 mmHg (some books say 36 to 46, some say 35 to 47...) by adjusting the rate and depth of breathing, raising the respiratory rate if the PaCO2 rises and lowering it if it falls.
Hyperventilation is when a person has a PaCO2 of below 35mmHg and is still breathing too fast, whether or not it was on purpose. | 
