I had dental surgery about 9 months ago, but the place I was at was kinda janky. Anyways, they had a dirty tool and nicked the roof of my mouth, and I ended up with a GIANT SORE on the roof of my mouth. It was about an inch all the way across, and caused a lot of other problems as well, such as massive swelling/ swollen lymph nodes, which made it difficult to swallow.
Another time I got something nasty is swimmer's ear/ a busted ear drum. I was swimming in 3 different lakes that weekend and I got to a pretty deep depth (about 29 feet), and I think my ear closed up and trapped water inside. The pressure may have even cause my ear drum to split. My ear was super achy for days and it was very difficult to hear. There was also a lot of pressure in there, and it hurt! Eventually when I came home and woke up the next day, the pressure was gone, but my pillow had lots of blood on it from my ear. I went to the doctors, and they couldn't explain all the blood because my ear was to swollen to see my eardrum. They said it possibly could have burst, but because they couldn't see it, they were just going to give me typical swimmer's ear medication.