Never thought this would apply to responsible me, but for one scary day in my life I cheated the horrid consequences of this. This was an hour after I'd eaten a huge meal during a long trip on a mostly empty rural highway. The calm monotone of the Book on Tape also had a lulling effect on me. At my first sign of nodding off, I should have pulled over until I could be more alert. Instead, I pressed on. Though I never drifted from my traffic lane, I recall jerking back to consciousness just in time to see I was about to slam into a truck that was stopped at a rare traffic light on the highway. My reflexes were just good enough to quickly throw my car into the empty lane beside me. I was hugely fortunate that lane was empty and that no cars were in the intersection I barreled through. Left me shaken for days, while I did some serious soul searching to how none of us are invulnerable. If this can happen to an otherwise careful driver like me, than most anyone can have a point in their life in which sleepiness can produce potentially devastating consequences. Take heed.
