All Emergencies - Basic life support principles:

1. Maintain an airway
2. Assess breathing
3. Monitor circulation

Management:

1. Terminate dental treatment.
2. Position patient upright.
3. A-B-C Airway, Breathing, Circulation - Basic life support, if indicated.
4. Remove dental materials from patient's mouth.
5. Calm the patient.
6. Have the patient rebreathe his or her exhaled air by cupping their hands in front of their mouth and nose.
7. In extreme cases where hyperventilation continues, IV diazepam or midazolam can be titrated slowly.

Source: Sedation, A Guide to Patient Management by Stanley F. Malamed