The answer depends in part on when the accident happened and at what point you may have had reason to believe that you had been injured. In if you are injured in an accident, you have two years from the time of the accident to file a personal injury lawsuit. The exception to this is when you didn't realize until later that you had been injured. In this situation, the "discovery rule" would apply. That is, you would have two years from the time you "discovered" that you had been injured before your statute of limitations would run out.
The discovery rule is important because not all injuries are immediately apparent after an accident. This can be particularly true for brain injuries like chronic traumatic encephalopathy (CTE), where symptoms may not show up until years later. If, for example, you or someone you love played football in the past, and now, five later, have begun showing symptoms like aggression, inattention and confusion, you may be able to file a lawsuit for two years from the time symptoms started to appear.
One challenge of the discovery rule, however, is that the clock starts ticking at a time when you reasonably should have known that you or a loved one had been injured. If, for example, in the previous example, the injured person started to show symptoms, but didn't file suit for three years from that point, it's possible that a court could decide that the statute of limitations had since run out. Therefore, if you or a loved one has begun to show symptoms of a brain injury, it's important to seek both medical treatment and legal advice right away to preserve the greatest range of options for medical and financial recovery.