First, move to safety and call 911 for an official police report. Take photos...

https://smart-wiki.win/index.php/What_If_Your_Injuries_Get_Worse_Days_After_a_Car_Accident%3F

First, move to safety and call 911 for an official police report. Take photos of the scene and grab witness info. See a doctor immediately to document your injuries, even if you feel fine