1-2mm is a LOT of play for a bearing. Are you saying that the crank slides that much or that you can see the bottom bracket moving? I would definitely get it looked at. Depending on the issue you could do irreparable damage to your frame.
EDIT: Also, what cranks do you have on your bike? It could be something as simple as tightening a couple of bolts on the cranks. Or maybe a bearing preload.