Your GP or Pharm should have given you more info. Lorazepam (Ativan) is a short acting benzodiazepine compared to something like clonazepam (Klonopin). Lorazepam typically last a few hours and 0.5 mg is not a big dose. If you are taking it before bed you should have no problem driving in the morning. However everyone can be affected differently by benzos so you will just have to see how you feel. Should not drink while taking benzos and should not mix different benzos together. Not sure exactly why you are taking them but whether it be insomnia, anxiety, etc not drinking at all is probably a good idea anyway.
I was just about to say that.