It happened this week after a 18 mile hike I found myself nodding at the wheel and I just took a new insurance course on safe driving..My dad was completly passed out. A very dangerous situation and you should not fight it when you are doing 55 mph. They had this list in the course.
These are the foods to avoid that are high in Triptophane (not in any order)
Tuna & Atlantic Perch
White Bread Flour
Milk
Rice
Figs
Peanuts
Soy products
Sesame seeds
Turkey,
Two things that really help if you are doing a long drive a Banana in the morning and if you find yourself nodding off is a Hot Chocolate or Coffee and a 15 minute stop. Don't forget to do the four second rule.
http://en.wikipedia.org/wiki/Tryptophan