Not an illness but it is a mdical condition in most cases but I am not sure about the carer. I would think most dissabled would accept it even if only to take a partner or mate with them.
I was told that to qualify for a disabled ticket, which incidentally includes a free carer ticket the applicant must be in receipt of the higher form of DLA. or have a letter of medical proof of disability from his/her doctor.
My son a STH in upper West had an operation on his leg and was confinded to a wheel chair for abour 5 games and I had no trouble getting a wheelchair ticket. They did say he had to apply for each game individually and they were in great demand. The other point to be taken into account is...