Well, I'll play Contrarian, here. OP, I think you should avoid fast pace line rides, altogether. Your auto accident heightens the risk, two-fold: impaired processing of visual data and increased likelihood that any future head trauma could be disabling. The benefits are simply, IMHO, not worth it.

Check into moderate- and "social"-paced group rides in your area and give them a try. The slower pace will make the tight formation less critical, increase your reaction distance, yet with the benefits of a group ride.