mysterious earthquake in boston?

Sunday night Erin and I were sitting on the couch, discussing our upcoming trip.  It was around 10:30pm.  Then I felt shaking like when someone is shaking their leg and it shakes the whole table or couch or whatever.  Some of our Christmas tree branches were kind of bobbing up and down too, so I looked at Erin's feet to see if she was the cause, but she was sitting still.  It lasted just for maybe 5 seconds, but there weren't any loud noises outside like something large going by or something hitting the building.  We tried to see if there were any earthquakes reported for Boston, but nothing came of our search.  So maybe it was only in our apartment.  Who knows!  So mysterious and strange.