Dear as said by you have severe neck pain with radiation to head and back and there is history of car accident also .All this is suggestive of musculoskeletal pain with or without some nerve compression . To confirm the diagnosis we need an MRI cervical spine .that will show us about any bone fracture or nerve root compression or it may be a simple muscle injury or stain..bone fracture with prolapsed disc compressing nerve is an emergency . That must be diagnosed as soon as possible and managed . If it is some muscle stain it can be managed conservatively by some muscle relaxant and pain killers along with physiotherapy . So at this time you need to discuss all this with your physician .hope this will help.