What just happened to my transaxle?

I was driving my '04 Matrix, and when shifting from 3rd to 4th, felt nothing. There was no noise or anything to indicate id just broken something, just didn't grab gear. The top end of the shifter (R,1,3,5) work normally, but the low side with 2-6 feels like there's nothing there. I can still upshift through those gears if my lever position is perfect, but I cant feel them engage- I don't know if i'm in gear until I let the clutch out. Any ideas?