First, get to a safe spot. Check yourself for injuries and see a doctor...

https://lima-wiki.win/index.php/What_If_You_Didn%E2%80%99t_Get_Witness_Names%3F_A_Paralegal%E2%80%99s_Guide_to_Reconstructing_Your_Claim

First, get to a safe spot. Check yourself for injuries and see a doctor immediately, even if you feel fine. Call the police to get an official report. Snap photos of the scene and grab contact info from witnesses