It doesn’t make you lose consciousness, but it effectively relieves you from pain. You may only feel slight pressure or movement. Local anaesthetic works by blocking the nerves from the affected parts of the body so that pain signals would not reach your brain.
A local anaesthetic is injected or applied on the area the dentist needs to work on—the gums, the inside of the cheek, affected tooth, etc. Upon administration of local anaesthetic, it will only take a few minutes for you to lose sensation in the area where it is injected or applied. Your dentist will make sure that the area is completely numb before starting the procedure. With most local anaesthetics, your tooth will be numb for 2-3 hours, while your lips and tongue will be numb for 3-5 hours after the time of injection. As the blood flow carries away the anaesthetic from the injection site to be metabolized or broken down, the numb feeling will gradually fade away. During this time, it is important not to sustain any damage to the numb area. One of the reasons why you are told to rest and take it easy after any procedure administered with an anaesthetic is because being active or engaging in any form of strenuous physical activity makes the anaesthetic effects fade more quickly.