I tried to take a picture of my 'face cancer', as I named the mystery bump on my left jaw (on the right, in the photo, obviously..) It's not that obvious in the picture, but it was very obvious IRL.
I had it checked, yesterday, although it had already more or less disappeared. Turns out that it was probably a temporary blockage in the left submandibular gland - the middle one of the three salivary glands on each side. (Yes, I had to google it when I came home..) Apparently, if it happens again, I should go back when it's actually swollen.
Btw, I discovered how to minimise the time spent in the waiting room - it seems that I just need to take my crocheting with me and pull it out of the bag, and I'll be called in immediately! =D (I was almost disappointed! I'd looked forward to crocheting a bit, while waiting to be called in..)