Blood alcohol testing is a test that will measure the amount of Ethanol in your body. Alcohol is instantly absorbed into the body and after one hour of drinking, it will have the highest concentration in your bloodstream. Depending on how much food you have ingested could cause this to happen at a slower rate but will inevitably still cause intoxication. almost all the alcohol that is ingested will be broken down within the liver and the rest is passed in urine or your breath. Hence why the main tests are Blood and/or Breath.
Depending on how much you have had, you will feel the effects of ethanol or alcohol in your system. If one was to indulge in large amounts of alcohol, you could have symptoms anywhere from slight dizziness to complete disorientation. If you have problems standing or walking, I can guarantee you that driving would not be a good option.