Tooth abscess and a cracked tooth, and a botched treatment from my usual NHS dentist in which included a weird/horrible experience with the injection process as well. It was months and further surgery via a private dentist paid for by money from my very generous grandmother before I was "normal" in any way again, and longer still before I recovered from the mental trauma. I don't think I'll ever really get over it, though and I think the whole thing contributed to the nervous breakdown I had that year. Still haunts me a bit and I can't think of 2016 as anything other than the worst year of my life.