You should hire an attorney any time you have serious injuries that require a significant amount of treatment and recovery. For example, if you have injuries that require a hospital stay and a few weeks off work, you should definitely hire a car accident personal injury lawyer to represent you. You will never be able to get as much compensation from the insurance company if you represent yourself.
Also, you should always have an attorney representing you if you need surgery or physical therapy. People who are not personal injury lawyers do not understand the medical care they will need in the future and will not get enough money if they negotiate a deal on their own. So, hire a car accident personal injury lawyer today if you have serious injuries.