Even i go thru these periods during my bike rides wherein im deep in thought abt something that when i do come out of it, im like "Whoa!, concentrate on the road dude or im roadkill." But no accidents so far, so i guess its just a matter of instincts and reflexes that help u make it thru the daily grind of driving ur car/bike.
Also from time to time, i experience a sense of deja vu as thebanik pointed out earlier. And i agree with motorheadinc's analysis. I always used to wonder why i felt that way and sometimes used to worrry that my mind's getting f'd up but im atleast glad that other peeps feel the same way too and that im not the only one. Seems like its alrite if u feel a certain amnt of deja vu.......