@TruckingSexy There are plenty of drivers who are allergic to manual transmissions, atlases, physical fitness, proper attire, pre-trips, maintenance, proper hygiene. They must be on some kind of prescription that combats self-awareness and they still have jobs. I think you will be ok.
The "D" part of Allegra D is simply Pseudophedrine, more commonly know as Sudafed. If anything this would make you more alert not less.