Prints Slowly Moving Over

Are your stepper motors binding, do you hear them grinding?

I'm at a loss, don't think I've seen that before, it's generally in one axis only.  Nothing else changed, have you tried other files?

I doubt its a code based issue, though bring up the file in repetier's gcode view and double check. I have mine home after every layer for redundancy, you could try doing that in the mean time. It might still wander, but it'll catch itself eventually.

Check your flow rate.  Sometimes when it offsets all over the place, it is because some plastic is curling up or getting smooshed up high enough for the nozzle to snag on it.  This can happen in any direction and give you skipped layers to any side.  It can be overhanging perimeters that curl  up and harden as they cool, or solid layers with too much extrusion, causing raised ridges between threads.

Oozing plastic can get smeared onto support as the nozzle travels over it.  Sometimes support is generated so thinly, that some layers don't stick and fall off to the side.  For every layer after that, the nozzle will be extruding plastic onto a spot where there is no lower layer to stick it to, so it gets wiped off somewhere else creating more rough patches for the nozzle to drag on.