Welcome, nquixote!

I am another one who doubts that you have a whiplash injury or a TBI from that slap you gave yourself.

Have you started with the obvious--by looking at your diet and at whatever meds or supplements you're taking? Quite often there's something in the diet or a person's meds that shouldn't be there or that is there in the wrong quantity.

Another obvious suggestion: sleep. Do you get enough sleep and is it fairly regular? Or do you stay up all night, maybe for a few days, then sleep nonstop for a day and a half? Some people routinely live like that, and it can cause a boatload of symptoms.

Those are just a couple of ideas you've probably already dealt with long ago. I hope you can find some answers soon.