Happy gas is nitrous oxide, which is used to relieve pain through inhalation.
After roughly 4-5 breaths the pain will start to ease and you will start to feel relaxed. It has no colour, smell, and doesn’t irritate. At a deeper level of sedation again, sleepiness, difficulty to keep one’s eyes open can occur.
The depth of sedation can be altered from moment to moment, allowing the person who administers the gas to increase or decrease the depth of sedation. Other sedation techniques don’t allow for this. For example, with IV sedation, it’s easy to deepen the level of sedation, but difficult to lessen it. Whereas with gas, the effects are almost instant.
Other sedation techniques have a fixed duration of action (because the effects of pills or intravenous drugs last for a specific time span); whereas gas can be given for the exact time span it’s needed for.