Field sobriety tests are not evidentiary certainties like a blood alcohol content test via a breathalyzer, so intoxication determined by the field sobriety test is open to challenges on multiple levels.  For instance, your intoxication may be called into question regarding what caused your imbalance and drunken appearance during the test.  If you take anxiety meds, for instance, you could throw doubt into the assertion you were intoxicated on liquor by saying you simply appeared off because you took your medication and was woozy therefrom.  Another tactic would be to say you were sleep-deprived.  Regardless, without a breathalyzer test proving intoxication, a field sobriety test opens up many possibilities to resolve your case on lesser charges than an OWI.