It's not normally possible, unless you have a leak somewhere. Well there could be some build up behind the caliper and thus why it might of been stuck. You'll want to take the wheels off and turn the rotors, with no pressure from the brakes, and see if you hear some rubbing (either from the pads or calipers). There might be some VERY slight rubbing from the pads which is okay, but there shouldn't be that much and it should be even throughout the whole turn. If there is rubbing from the pads and it's not even throughout the turn then you better fix that or you'll get a flat spot on the rotor which will feel like warped rotors. There shouldn't be any rubbing of the caliper on the rotor. Is there any noise from the brakes when you ride without applying the brakes? How old is the fluid? Is the fluid clear/clean? If not then I would recommend on replacing it.