How frequently do people vomit at the dentist?

Almost never!: It just does not happen very often. Extreme apprehension and severe gag reflux could trigger the response.

Uncommon: Happens most often when taking impressions, and more often in kids under about age 10. If you are concerned discuss w Dentist. Many techniques exist for making you comfortable. For example, schedule appt 1st thing AM, and go in with an empty stomach.

Happen occasionally: A hyperactive or sensitive gag reflex can be a problem at the dentist. If you have a sensitive gag reflex, let your dentist know before the dental treatment.

Rarely: Causes for regurgitation in the office are usually a heavy meal prior to the visit and sometimes overuse of nitrous oxide/oxygen analgesia. I can remember 2x in over 35 years in my office and not in the last 25 years.