When your health insurer pays for your medical expenses for treatment caused by someone else’s negligence, and you ultimately recover monetary damages from that negligent person, your health insurer has a right to be reimbursed (these are called rights of subrogation) from you out of the accident money you received.
Here is the reasoning - Your settlement money from the negligent driver’s insurance included payment to you for medical bills resulting from your treatment. But your health insurer also paid you (by paying the health care provider) for those same medical bills.
To allow you to be paid for the medical bills, while also having your own health insurance pay for those same bills, is the legal equivalent of “double dipping”. Instead, your health insurer has a legal right of subrogation (i.e. right of reimbursement) that requires you to reimburse them in the amount they paid on your behalf for treatment resulting from the accident.
Keep in mind, if you do not ultimately make a recovery from the responsible driver, either because they didn’t carry insurance, or for any other reason, you would not be required to reimburse your health insurer anything. Your health insurance company’s subrogation rights are triggered only upon your receipt of monetary damages from the negligent party.
This answer provides a simple explanation, but there are often more complex factors involving subrogation rights, including the amount that must be reimbursed. For this reason, we recommend seeking legal counsel to help ensure all of your legal rights and remedies are considered when dealing with issues of reimbursement.