Can you tell me how can laughing gas work ?

Nitros oxide: Displaces the oxygen in your system giving you a euphoric feeling(like having a couple glasses of wine) and it is totally out of your system within minutes of getting room air. It is a mix of oxygen and n2o. See your dentist and ask for a sample.

Analgesic...: The main reason why nitrous oxide is used by dentists is that will cause a slight analgesic action and the patient won't feel minor "injuries" as the needle pinch, for instance. At he same time the patient (most of them) will be distracted due to the "good" feeling that causes. When patients are afraid of the gas, I do not recommend it, as it will cause undesirable symptoms. Very safe to use.

Mild sedation: Nitrous oxide/oxygen is the weakest of all anesthesia gases used today. It will produce a level of analgesia (increased tolerance for mild pain) by way of the central nervous system and decrease anxiety. It should produce it's effect at around a 20- 40% concentration and should be administered with oxygen. It takes 3-5 minutes to clear and you should be given 100% oxygen before and after.