Dan,

It sounds like you have a good idea of the triggers (level of impact or shaking) and what to do after. You may never find the actual cause/injury. That does not mean you can't stop these relapses. Learn new behaviors to limit these impacts and shaking events. It may take some time to develop a tolerance for head movement. It took me quite some time.

I have to be careful riding in cars. I have explained the techniques I use to limit the shaking. We actually test drove cars over railroad tracks and other bumps to see how I responded to the bumps.

I have a horrible time with speed bumps even at a slow speed.

Try to keep track of the situations where you are exposed to bumps and shaking. Post them and I will comment about any things I do to limit the impact on my brain.

My best to you.