Need help with Anti Lock Brakes, ABS - 2001 Chevy Malibu...

A dash warning light appeared about 3 days ago that something might be wrong with my anti lock brakes, I immediately pulled over, read about the warning in my own manual, it said turn the veh off, then restart it and if the light doesn't reappear all is probably OK but if the light comes back on then have it checked out. I have been noticing that my brakes don't seem to stop me as quickly as before, then the light came on, I still have brakes like the manual said I would have, but does anyone know if it might be a serious expensive and/or dangerous situation. I plan to take it in tomorrow to a Goodyear shop and have them look at it.