Emergency Root Canal Treatment!
I had that on Monday (yesterday), because of one of my bottom front teeth. Luckily, it wasn't very painful. The nerve of the tooth was mostly dead, and the anaesthetic worked a treat anyway.. I didn't even dribble my water afterwards!
I'm sure I could have gone without pain meds today, but as the day wore on, my overused mouth was starting to make itself known, so I decided to take a paracetamol+caffeine (for the caffeine, really!) and later an ibuprofen tablet as a preventative measure. I'll probably also take one just before I sleep, so there's less chance of me waking up.
Apparently dead nerves/gum infection usually occurs because of some prior accident, and the only accident I could recall happened when I would've still had my baby teeth, so that's almost certainly not the cause. So, no idea why!