I dream that my gf gets hit with a car or something.. i keep having nightmares about it.. why won't this stop?

Nightmare disorder: Please see a psychiatrist who also specializes in sleep disorders if you can. It sounds like you have a nightmare disorder but you could haveptsd. Treatment is usually prazosin to stop the nightmares. If you have post traumatic stress disorder the psychiatrist will also recommends psychotherapy. Most people with pure nightmare disorder do not require psychotherapy.