Call the police and report the event. This report will be valuable afterward.
2. Capture as many images as you can of the participating cars. Try your best to approach from different distances and elevations.
3. Visit your doctor when you get home. It is best to have medical records on hand when the occurrence occurs. It's never a good idea to see a lawyer before a doctor.
4. Get in touch with a car accident lawyer who can submit a claim on your behalf.