Will,

There is a correlation between neck injuries and concussion but you can not label either as the only or primary cause. In your case, I suggest you have two problems. First, your concussion history makes this last concussion more problematic. Second, your neck causes its own symptoms and it exacerbates your concussion symptoms.

Both need to be treated simultaneously. The neck requires strict postural discipline, especially when sleeping. Reduce the inflammation when awake. Sleep in a way that does not cause neck inflammation. Get treatment for the neck, i.e. gentle manipulation/mobilization with gentle traction, avoid Range of Motion exercises that push for increased ROM,

Take all of the stress reducing steps to allow the brain to rest and heal. Deal with your anxiety issues. Proper nutrition, etc.

Now, plan on doing this consistently for the long term. Slowly, you should see improvements. Reduce the risk of relapse. A few weeks of 2 steps forward with the occasional 1 step backward can quickly be undone with 1 'pushing it' step forward then 4 steps backward.

You need to manage or moderate your recover, not try to force it.

Regarding the neck, very few professionals will ever be able to diagnose a neck injury. Concussion neck injuries are very subtle. Treat the neck like it has been injured even though you can not pinpoint the injury. Just a bit of soft tissue trauma can cause inflammation that can exacerbate head aches and other symptoms.

I diligently work to avoid bad neck posture. It is now a life habit.

You should try to do the same.

My best to you.