The Collaborative International Dictionary of English v.0.48:

hyperventilation \hyperventilation\ n.
   1. The act or process of hyperventilating; breathing rapidly
      and deeply.
      [PJC]

   2. (Med.) A condition in which alveolar carbon dioxide
      concentration is markedly lower than normal, usually due
      to breathing rapidly and deeply.
      [PJC]

WordNet (r) 3.0 (2006):

hyperventilation
    n 1: an increased depth and rate of breathing greater than
         demanded by the body needs; can cause dizziness and
         tingling of the fingers and toes and chest pain if
         continued