I had crippling anxiety for about 8 years after my first brain injury. It didn't ever go away on its own, but I found interventions that helped. Therapy helped me a lot, especially EMDR therapy for the lingering psychological trauma from everything that happened. Neurofeedback helped me a ton as well. Neither of those options are probably necessary though for anxiety that may well be just a PCS symptom rather than psychological. Have you tried the herb ashwagandha? I take it most days and it has lowered my anxiety quite a lot. It's not very expensive.

Good luck!