Driving for a long time can be boring, especially at night or when you drive at the same speed for long distances. You can become "hypnotized" where everything seems to float by and you pay less attention to what is happening around you. You may even fall asleep.

You can help prevent highway hypnosis by following a few simple rules:

o    Don't eat a heavy meal before you drive.
o    Wear comfortable clothing.
o    Talk with your passengers, but not to the point of distraction.
o    Keep your eyes moving and check your mirrors often.
o    Take an interest in all road signs and traffic around you.
o    Take a coffee or walking break every hour.
o    Don't try to drive too far in one day.
o    Avoid driving during your normal sleeping hours.
o    Keep the temperature in your vehicle cool.

If you do start to become drowsy, do something different immediately. Open a window; talk to passengers; sing out loud; move your body around a bit.
Stop at the next service centre or rest area and take a short walk or have a coffee and eat a light snack. If you don't feel any more alert, find a place to sleep for an hour or for the night.

Reference:
http://www.mto.gov.on.ca/english/pubs/drivhand/carvan.htm