There is nothing that says that the police cannot interrogate an injured person; and moreover, the police may not have even known the extent of your injuries at that moment.That said, if they used any statements you made at the time against you, you may be able to get them thrown out on the basis of either or both 1) you were not competent (due to the concussion) to understand your rights and give a statement; and/or 2) you were under duress (improper pressure) because the circumstances could have led you to believe that you would only receive care/treatment once you spoke to the police.And if any delay in the police extricating you from the vehicle or otherwise providing treatment exacerbated your injuries or caused you additional harm or medical expense, you may have grounds to sue the police and the employer (city, county, or state) for your additional injuries and costs.