Did your APR suddenly jump up? Hit with a charge for being late on a payment? When things like this happen many consumers just tend to let it slip by. But as long as you don't make a habit out of it you can usually get it remedied by simply calling up the credit card issuer and asking if they would be so kind as to make an exception this one time.
http://consumerist.com/5136750/nice-letter-gets-chase-to-reinstate-mans-promotional-apr