First point, You should be allowed to defer for another year. This deferment would be considered a "Reasonable accommodation for your disability."

Go ahead and follow through with the SSDI process. SSDI will require that you be assessed in 3 to 5 years to see if you have improved. You can always become non-disabled. Until then, you will have some breathing room to work on the academic skills you will need for the OTA program.

You can also consider getting degreed in Social Work so you can become a case manager for people with TBI. It can be just as productive as the more hands on OTA. There are things a Social Worker can do that fill in the voids left between OT, PT, RecT, etc.

You experience with mTBI will be a great asset to your career.

If you get approved for SSDI, you can still work and make up to $1000 per month. This could be a way to take a slower path to the career you want.

My best to you.