If you get drowsy while driving it is best to:

While driving, once you get drowsy or sleepy in a certain time, it is best to stop the car immediately or to a nearby spot where you can park your car, then you should get out of the car and start walking around a few times, until your drowsiness is gone. Getting drowsy while driving is dangerous, you might end up falling a sleep and cause an accident. It is best to hinder yourself from getting drowsy.