> I had fallen asleep with my eyes open but was staying upright in the driver's seat, maintaining my speed and staying on the road. It was an extremely frighten

> I had fallen asleep with my eyes open but was staying upright in the driver's seat, maintaining my speed and staying on the road. It was an extremely frightening experience, because I was very keenly aware of not being conscious a few seconds earlier, and having no sense of how much time had passed. I don't know your specific story, but this is not to be confused with the hypnotic state that one usually enters when doing something routinely (e.g daily commute) and the brain simply drops the irrelevant information before it reaches you consciousness. Then something unusual happens that crosses the relevancy engine (a pattern, a sound, anything) and the brain plugs itself back into conscious mode just in case the situation might ever so slightly require highly cognitive decision-making functions. In those cases consciousness can drift away and think about what you'll be having for dinner or some project you're working on. When consciousness snaps back into the driver role you'll have no idea of how much time has elapsed or even which road you took.