I used to have dreams that would scare me despite their content being mild. I don't know much about any sort of medication, so I can't say that that's the cause of the dreams. Perhaps if you are depressed in your waking life it can have effects on your dreams, so I would probably talk to your doctor about the upsetting dreams, depression and the medication's side effects.

Otherwise I would think that something else is troubling you in your waking life and your dreams are trying to get you to acknowledge that. Perhaps you are insecure about your ability to drive (on a subconscious level at least) since the accident, and this particular dream is affecting that. Perhaps you could talk to a friend about how the car crash affected you?

Just suggestions.