I do this on a daily basis driving to work but never from work. I live 1 hr 15 mins away from my job. When I do fall asleep then wake up i just fall asleep right after again. like a cycle. I cannot help it at all. Ive tried everything from loud music, cold air from opening the windows, to slapping myself in the face. Nothing works. I feel like I get enough sleep at night (at least 6 hours). It has happened while someone else is in the car with me. I'm not on any meds and I'm never intoxicated while driving. My eyes feel heavy but not the normal sleepy heavy. Its almost like they want to cross. I feel that my eyes are open when I fall asleep in this manner. I have experienced this on a very rare occation while talking on the phone to customers but when that happens and I wake, I dont fall sleep again.