The only answer anyone can really give you is “what does it mean to you?”

Dreams do not have consistent meanings amongst people with similar dreams. The bigger question is “do dreams have any meaning at all”. No one knows, and anyone who says they know with certainty is false.

I have found that the emotion connected to the dream is much more meaningful than the visuals. This could well be a manifestation of anxiety.

“Car Accident
To dream of a car accident symbolizes your emotional state. You may be harboring deep anxieties and fears. Are you “driving” yourself too hard? Perhaps you need to slow down before you hit disaster. You need to rethink or re-plan your course of actions and set yourself on a better path.” Dream Moods

It’s the “calm down” bit that interests me, maybe you crashed the wife’s car & she’s about to deliver a glancing blow to your bonce with a medium sized saucepan.
That being the case, i’d suggest relationship troubles are afoot.

There is some disaster looming in your life and you are urging yourself to calm down. It’s an anxiety dream. You want to learn to be more calm. Good luck.

Whatever the dream seems to mean to those who can glean meanings from them, it seems to me that you’re giving yourself excellent advice during the execution of the activity. Namely, “Calm down!”, and following that, “Wake up!” are pieces of advice that many more should emulate.

Carry on.

It’s your subconscious mind expressing fear and anxiety. What do you feel fearful of and not in control of in your waking life? What “accidents” do you feel are waiting to happen?

In dream symbolism, car crashes represents sex. Telling yourself to calm down is like thinking about baseball.