So I'm not crazy. I woke up a little after 4:30 this morning, with the sensation that the house was rocking. I jumped out of bed to investigate, but found all well and normal.
Turns out it was a 5.2-magnitude earthquake.
Post-Dispatch and Tribune-Star stories here.
The U.S. Geologic Survey Web site says the quake was centered near West Salem, Ill., or about 40 miles northwest of Evansville, Ind.
...
The quake occurred in the Illinois basin-Ozark dome region that covers parts of Indiana, Kentucky, Illinois, Missouri, and Arkansas and stretches from Indianapolis and St. Louis to Memphis, according to the U.S. Geological Survey.
Also, apparently, the quake was felt in Grand Rapids, MI,, Cincinnati, OH - and even 450 miles away in Des Moines, IA.)
Of course, I couldn't get back to sleep - so I'm going to be a bit tired today!