You have heard of people who spleep while they are driving. But Parley P. Pratt one of the old Mormon missionaries from the early days of the Mormon Church tell us what happened with him while he was running from his enemies.
“At length the day began to dawn, and I must soon be under the necessity of hiding in the thickets, or making deviations from the road, in order to avoid discovery in passing the settlements. I, therefore, wished to push my way with all speed while it was yet too early for people to be stirring; but sleep now completely overpowered me. As I was walking along the road I could scarcely open my eyes for a moment to look my way for a few rods ahead, and they would then close in sleep in spite of all my powers. I would then proceed a few paces in my sleep till I stumbled, or till I had need to take another look at the road before me; then I would open my eyes and take one glance, and the lids would fall again as powerless as if I had no life. In this way I walked on, alternately sleeping and waking, till, I presume, I had more than fifty naps without ceasing to walk; and each time I opened my eyes and came to my senses I firmly resolved to keep them open and run no further risk; but while this resolution was still passing in my mind sleep would again steal over me, not exactly unawares, for I realized it each time, but had no power to prevent it.” (Parley P. Pratt, Autobiography, Chapter 34)