On rare occasions, people have reported a bad experience with nitrous oxide. Usually this is due to oversedation – getting too much N2O in the mix.
This is easily reversible by reducing the amount of N2O. For example, a few people have reported auditory and “physical” hallucinations, dizziness, or vertigo. Don’t panic if you should experience this.
While these symptoms are usually due to the N2O concentration being too high for you, the machines used nowadays have built-in safety features preventing an accidental overdose. Nonetheless, these sensations can be unpleasant – let your dentist know asap about any unpleasant sensations or symptoms so that they can adjust the percentage of N2O.
Laughing, becoming giddy, crying, or uncoordinated movements are other signs that the NO2 concentration is too high, but these will easily be spotted by your dentist. Alternatively, just rip the mask off your nose!
Don’t confuse “dizziness” with the normal feeling of lightheadedness which many people who’ve never had N2O before experience after maybe 60 or 90 seconds. The feeling of lightheadedness will pass as the concentration of N2O is increased. Some experts in this field (e. g. Stanley Malamed) argue that nitrous oxide should always be “titrated”. This means gradually increasing the percentage of nitrous oxide in the N2O – O2 mix until a comfortable level is reached.
The reason why titration should ideally be used every single time is because of potential adverse effects in the event of oversedation (including flashbacks of traumatic past events, as well as physical ill-effects). However, other experts (e.g. Fred Quarnstrom) say that it’s ok to use a mix based on prior experience (a concentration which a particular patient has experienced as pleasant during previous appointments).
Quite a lot of dentists do this because it’s quicker. The problem with this approach is that tolerance can vary from visit to visit, depending on both psychological and physiological factors. What is experienced as pleasant varies from person to person and from day to day.
And once a person has been oversedated, they may come to dislike nitrous oxide so much that they don’t want to try it again.