Earthquake!
Yup, we felt it!
Dan and I both woke up around 4:30am, after I heard creaking in the apartment like someone was walking around the hallway (which really disturbed me more than anything), and then our bedroom door (which was cracked) swung open. Then I noticed the bed was shaking! We just thought it was the wind, since we had some of the windows cracked, but there really wasn't much wind last night (and I didn't really question the logic of the wind making the bed shake). Totally crazy. I guess (at 5.2) it was the second largest ever recorded in this area.
UPDATE: Dan just phoned to say he felt an aftershock at the apartment just now (10:15am). Didn't feel it in our building in Evanston, but we're so tall, it probably sways enough as it is during a regular day.