When I was doing both it didn't take me long to make the connection between yawning all morning and... having driven the car. One thing I liked was the whole idea that if I woke up on the wrong side of the bed, though, or something made merun late... boing, I could just take the car and make it up. No stress or running around.
I think that sort of set me up so that when that happens now, I call in and say "I'm going to be late." (How late? Long as it takes to get this shoe out of my wheel... ) Then I stop stressing. (Fortunately, for the most part, nobody's world ends if I'm running late.)