I had horrible anxiety/panic attacks for the first 2-3 months, I think most of it was caused by lack of correct information about my injury, and me thinking that there's something horribly wrong with my brain, etc.
At first I didn't even realize that I was having these anxiety attacks since I've never had them before, I thought it was part of the concussion symptoms.
I would strongly recommend trying natural remedies for anxiety attacks first, before resorting to meds. I think that Xanax messed me up, and made it worse after I got used to it.