Narcolepsy While Driving

Hi, I just discovered this forum through a quick Google search. I wouldn't say I typically have any sleep problems - usually, I can fall asleep without much problem and sleep deeply in most situations. I am about twenty and fairly healthy.
For the past three days, I have had sudden sleep attacks while driving home from work. My commute is between 45m to 1hr in stop and go traffic and I think the monotony of driving in that environment as well as the warmth of the car is combining to make me very sleepy. I never feel tired before leaving the office and in fact I don't start feeling sleepy until 15 or 30 minutes into the drive.
I have tried blasting the AC, turning up the music, singing along to the radio, dancing, and slapping/pinching myself, but inevitably I will get so tired that I start slipping in and out of consciousness. Today, I drifted off for long enough to cross halfway into another lane until I woke up.
Does anybody experience the same thing or something similar? If so, how do you prevent yourself from getting sleepy or deal with it afterward? The only thing I can think of if a sleep attack happens is to pull off the freeway at the nearest exit and take a nap.