Nick,

SSDI will ask for your medical records but they do not rely on your doctors' determination of ability to work as in a Disability Rating. Your diagnosis of condition and medically directed work limits will be considered as a basis for their determination of what work you can do.

crystal,

winic1 is incorrect with her comment < just whether you can hold a job at a reasonably equivalent level to what you had before--so if you were a research chemist, they can't disallow you disability because you could sweep floors, still.>

State Disability and Private Disability Insurance may use the "disability to do equal work" as a factor. This is based on past payroll Disability Insurance contributions qualifying you for benefits to maintain the same income levels.

Social Security goes by a determination of whether you can sustain "substantial gainful activity." That means "can you hold a job that will pay in excess of $1000 per month, even if it is sweeping floors."

Some of the factors that usually apply with Post Concussion Syndrome are :
inability to maintain attention to a task
inability to tolerate a work environment
inability to receive and follow instructions, including multiple step instructions
inability to maintain proper social behaviors and inability to work successfully with others
inability to show up for a normal work schedule , i.e. good and bad days

There are a few other things that will be brought into the equation depending on the investigators handling your claim.

The initial application can be started online at SSA.gov. You can start it an log in from time to time to continue filling out the application. You can also schedule an appointment at the nearest SSA office for assistance by an in-person claims agent. Starting the online application gives you time to find all of the information at your own pace.

Give it a shot. You can always ask for help.

My best to you.