Exposing an impacted tooth is a surgical procedure that involves going through the gum and sometimes removing a little of the bone around the tooth. The operation is done under local anaesthetic (i.e. the patient is awake but feels no pain). A few stitches are often placed in the gum, and these are removed after a week. Once the anaesthetic wears off (2–3 hours), you can expect pain in the area of the exposed tooth, and sometimes swelling of the gum and even slight visible swelling of the face. There is pain because you have a wound in your mouth, but it eases with painkillers. The discomfort lasts from 3 days to a week.
This answer is for general information. Your own case needs an examination by an orthodontist.