Slow down.......take things one step at a time. No one on the web is going to be able to diagnose what you have from your description. You are doing the best thing already, which is going to see your dentist right away. There is no reason to leap all the way to cancer, when there are so many other things this can be. You may have an abscess on one of your upper posterior teeth that is causing the swelling and discomfort for instance. It could be a benign cyst. There are lots of choices that are more likely than cancer. Your dentist will be able to determine if it is either of these from an x-ray while you are in his office. It is unlikely that an oral cancer would develop this quickly from a few sore spots in the posterior of your palate into a large swelling in a day.

As to what a biopsy is like, it can range from something as simple as the dentist rubbing a small brush on the suspect area to pick up cells for examination, to him cutting a little piece of tissue from the area. Neither one of these procedures is anything to be concerned about. IF a biopsy is done, it will only take a few days for the results to be returned to the dentist from the pathology laboratory.