I do not carry an kind of notes. I will tell the ticket agent that I has severe claustrophobia due to a head injury. This usually gets their attention. I tell them that as long as i have visual space, I will be fine. But, If I have seat backs in my face, I will struggle. The worst is seeing the rows of seat backs and tops of heads. It is just too much visual stimulation. Trying to sleep is my safety valve if I get in trouble.

Having the slip of paper printed on the computer and nicely formatted gets the point across nicely. You will need to explain that you have no problems sitting in an exit row because many bulkhead seats are nearest the exit so need exit row qualified passengers. All that means is that you are ambulatory such that you could lift a piece of carry-on luggage over your head like you would to put it in the overhead compartment.

I have done lots of airline travel since my injury. Learned all the tricks.