(HealthDay News) -- Fainting occurs when the brain temporarily doesn't receive enough blood, says Mayo Clinic.
Fainting may have no known medical cause, or it can be a sign of a serious disorder. Because of this, always treat fainting as a medical emergency, Mayo says.
If someone faints, Mayo urges you to:
If the person isn't breathing, begin CPR and call 911. Continue CPR until help arrives or the person begins to breathe.