You are not alone. Many many victims of motor vehicle accidents say the same thing. In fact, a medical diagnosis exists addressing this very problem: “Traumatic Amnesia”. As descirbed, even a relatively “minor” car accident in which the occupant suffers only mild whiplash symptoms, can result in an ‘interruption in the short/long term memory transfer mechanism.”
What this means is, that if you don’t remember details about your car accident, it is probably normal and may indicate potentially more serious problems associated with a mild Traumatic Brain Injury.
The lack of the ability to recall the details of the accident also means that it may be difficult (or certainly more difficult) to prove who did what in terms of accident investigation, insurance claims, or a courtroom. If you have sustained an injury like this, and have no memory of the collision, it would be advisable to insist, at the scene, upon a formal accident investigation by a peace officer. It would also be advisable to mention these symptoms to a physician so that other symptoms of a closed head injury (dizziness, nausea, personality changes, among just a few) can also be assessed.