Something that has happend a few times is looking up and seeing a car coming from the opposite direction across the centerline of a road. Most of the time they wake up ad jerk back over into their lane. But I can think of a couple times that they did not. On one occasion my brother was driving behind me, saw me swerve me Right and managed to get over on the shoulder himself; he complimented me on my reflexes. Another time I got over to the Right but the car behind me swerved into the trees. You never know if this time is the time to panic.