If you feel a very strong urge to drive off the road or jump off a cliff, I would suggest a meeting with a therapist.

On the topic at hand, the Human brain evolves to have these kinds of thoughts. It allows you to simulate and prepare for unexpected situations. Basically, if you are driving then there is a chance that you might lose control and go off the road, so your brain urges you to think about the situation. So in the unlikely case that you actually go off the road, you're already prepared for it.