I suffered a lot of anxiety about relapse from minor head bumps during my recovery. I did the same thing you did - hit my head against the car hard enough to send me into a panic about relapsing or making my symptoms worse. I did have one hell of a headache for about 2 days afterwards, but it wasn't as bad as I thought it would be. I don't think that level of trauma is enough to seriously put you behind, but good luck anyway!