How do you treat a person suffering from hyperventilation?

Depends on the cause. if it's just hysteria,have person sit on the edge of chair, scrunch top of paper bag and hold over persons mouth. In a calm voice, tell them to take deep, full breaths and try to relax. Reassure them that they can control this. If they have suffered any trauma,a fall, a blow to the head ,neck, back, side or abdomen, go to ER. If they have had any recent respiratory problems, are on any meds,prescription or OTC, go to the ER. If this is a recurrent problem, may be indicative of anxiety disorder and needs evaluation by a DR. When in doubt, better safe than sorry. This advice applies to normal adults only. Never take a chance with children,the elderly or anyone mentally challengened in any way.