Have a technician with a block test kit inspect your vehicle. What he will do is check your coolant for CO or CO2. He will use a dye and a plunger device to extract vapors from the hot coolant in the radiator to see if there are any trace vapors. The head gasket can also blow out very hot cumbustion gas and cause you to leak coolant out of your over flow reservior. Please try and have an ASE certified technician do this. This is not something for your local shade tree or the partially trained "speed shop" "mechanic." Find an experienced shop with properly trained technicians and you'll get what you pay for and vice versa.
Art Zarate Jr.
You'll still be able to drive you car and you won't feel much aof an abnormality with this type of gasket problem, but I would have it taken care of imediately.
93 Cobra - rebuild in the works
ASE master, Ford Master certified technician, I specialize in all electrical, driveability, engine performance, custom stereo designs, and getting my customer complete satisfaction with their build.