The TBI specialist is ignorant. The subtle instability in the upper neck is not diagnosed by imaging or range of motion or other criteria. It is diagnosed by treating it and seeing if conditions improve.

There is no comprehensive NeuroPsych battery with a single score like 14/15. That was worthless. Was that a computer scored test?

Higher IQ people tend to be more sensitive to minor changes in function.

Read about the Buffalo protocol. It discusses how to moderate exercise to an intensity where the pulse stays 10% below the headache and other symptoms threshold.

You need to work on this. "I'm also easily stressed (single, poor social support, high standards)"

Nobody else can help you with this. You have to make your own choices about how you want to live your life. Most of us have found a moderated life is much more successful and consistent. Don't blame ADHD. That is not a blamable condition because it is not changeable. We are who and what we are. We must live our life in that context.

You have prolonged symptoms of concussion. That is not changeable. You can only learn to moderate and manage your life. Your high standards need to be moderated to fit your current condition.