Nitrous oxide is a safe and effective sedative agent that is mixed with oxygen and inhaled through a small mask that fits over your nose to help you relax. Nitrous oxide, sometimes called “laughing gas,” is one option your dentist offers to help make you more comfortable during certain procedures. It is not intended to put you to sleep. . You may feel light-headed or a tingling in your arms and legs. Some people say their arms and legs feel heavy. Ultimately, you should feel calm and comfortable.