Travism,

Welcome to NeuroTalk.

From your head injury history, it is highly likely you have suffered many more concussions that you have counted. Plus, you have a lifetime of sub-concussive impacts. This leads to Multiple Impact Syndrome which is basically prolonged PCS or even lifelong Post Concussion Syndrome. Your personality struggles are likely with you to stay.

In my experience and understanding, the only things you can do now are two fold.
First....Take good care of your brain. This means brain oriented nutrition like the vitamins and supplements regimen in the Sticky at the top.
Second.. Learn some behavioral strategies. You don't say but I would expect that you have a tendency to over-reacting when you are in these shut down modes. Many of us tend toward outbursts in these situations.

How long do these shut down periods last ?

They can be indicative of a sort of seizure like event. I struggled with these during my high school and college years. They can also simply be a retreat due to overload or over-stimulation. Reducing your stimulation levels and exposure can make a big difference.

You may want to check with your college to see if the recent NCAA concussion settlement can help direct you to some specialized care. I would highly recommend it. I struggled through my 20's and 30's without help then the world came crashing down in my early to mid 40's. You may find your struggles increasing as you get older and approach your 40's.

My best to you.