Oh yay. Feels like somebody kicked me straight in the mouth; so for those who wish that upon me, congratulations: root canal, FTW!
Dentist says it's the result of having done The Right Thing some 25 years ago when I had this crown installed. Apparently, nerve death and infection often ensue after some random period of time.
So, once again, no good deed or right action goes unpunished. Such intelligent design. Such planned perfection and splendor. ;-)
Get to wait until Thursday for the root canal.